Fourth wall

The fourth wall is a term used to describe the imaginary wall between the audience and the stage, or in this case the gamer and the video game. The term derives from a movie or television set having three walls; the fourth wall is the camera. In effect, it is the separation of the real and the imagined.

The origin of the term the fourth wall was first used in theater, where actors would acknowledge the presence of the audience through actions or speech. In the video game world, the fourth wall is often addressed in a humorous manner. In the early days of gaming, such things as putting certain information not available in-game in instruction manuals or on box art were rudimentary forms of software piracy prevention.

Origin
The term "fourth wall" stems from the absence of a fourth wall on a three-walled set where the audience is viewing the production. The audience is supposed to assume there is a "fourth wall" present, even though it physically is not there. This is widely noticeable on various television programs, such as situational comedies, but the term originated in theater, where conventional three-walled stage sets provide a more obvious "fourth wall."

The meaning of the term "fourth wall" has been adapted to refer to the boundary between the fiction and the audience. "Fourth wall" is part of the suspension of disbelief between a fictional work and an audience. The audience will usually passively accept the presence of the fourth wall without giving it any direct thought, allowing them to enjoy the fiction as if they were observing real events. It is the invisible barrier between realities.

The presence of a fourth wall is one of the best established conventions of fiction and as such has led some artists to draw direct attention to it for dramatic effect. This is known as "breaking the fourth wall."

Fourth wall references in the Metal Gear series
The Metal Gear series is notorious for breaking the fourth wall. Sometimes the fourth wall is broken on many occasions in a single game.

Common elements

 * The main character's support team will describe actions using terminology such as "circle," "square," and "action button," referring to the game controller in use. They are also able to see what the main character sees, does, and what weapon or equipment he is using.
 * Gaming magazines featuring Metal Gear games can often be seen.

Metal Gear

 * If the player has the maximum amount of rations/ammo, when Solid Snake attempts to pick up some more, he will say "I can't carry any more."
 * Just before the player learns that Big Boss is the commander of Outer Heaven, Big Boss will call and order the player to abort the mission and turn off the game console.
 * During Snake's fight with Big Boss, Jennifer tells Snake that using a cigarette will buy him more time to escape Outer Heaven, by slowing down the timer countdown of the self-destruct sequence.

Metal Gear 2: Solid Snake

 * Like in Metal Gear, if the player has the maximum amount of rations/ammo, when Snake attempts to pick up some more, he will say "I can't carry any more."
 * After the player reaches the Tower Building, Colonel Campbell calls and tells Snake that he is changing his radio frequency. In the MSX2 version, he says that the frequency is on the rear side of the game's package. In the Metal Gear Solid 3: Subsistence version, he says that the frequency is in a picture in the game's manual. However, there is actually no picture in the manual.
 * Campbell tells the player to use a tap code found in the game's manual in order to decipher radio frequencies. The Subsistence manual does not have any information on how to decipher tap codes.
 * Master Miller will tell the player not to envision the Game Over screen upon making a mistake while describing the power of positive thinking. He will also advise the player not to drink too much soda while playing nor play the game immediately after eating in order to avoid loss of concentration.
 * Campbell will tell the player to think like the game designer in order to see possibilites that are not immediately obvious. He also advises the player to fight only when one has to fight, which are "the rules on the battlefield, in a shooting game."

Metal Gear Solid/The Twin Snakes

 * The player must find Meryl Silverburgh's frequency using a screenshot on the back of the game's packaging. In The Essential Collection version of Metal Gear Solid, her Codec frequency is in the manual. It's also featured on the back of the collector's box, due to the Kojima Productions logo put on the back of the game case. In the PlayStation Network version, it is in the game's digital manual.
 * Master Miller warns the player to use the bathroom frequently so as to not miss one of the game's cutscenes, and to not play while tired, after eating or after a bath. He also advises the player to trust their instincts as a gamer and think as a map designer.
 * During a scene before the Psycho Mantis battle, while Snake is talking to Meryl, the music cuts out and Snake says "What happened to the music?" However, Naomi later says "that tune is his mind control music."
 * Famously, the battle with Psycho Mantis repeatedly breaks the fourth wall. During the player's battle with him:
 * Psycho Mantis reads the player's memory card. If the player has corresponding Konami-based save files, Psycho Mantis will comment on them (e.g. "You like Castlevania, don't you?"). Mantis also does this in The Twin Snakes, although with Nintendo game saves instead (such as Super Smash Bros. Melee or Eternal Darkness: Sanity's Requiem). And if the player doesn't have anything on their memory card (or anything Mantis recognizes) he'll say that "your memory is completely clean."
 * Psycho Mantis tells the player to place the game controller on the ground and that he will move it with the power of his mind. In The Twin Snakes, Snake physically turns to face the camera, and nods approvingly to the player.
 * Before the fight, Mantis will check to see how many times the player has saved the game. If the player has saved less than three times, Mantis will say, "You're somewhat reckless." If the player has saved more than three times, he will call them prudent.
 * Mantis will also comment on how the player has progressed during the game up until their encounter. If the player has successfully avoided enemy traps, he will comment, "You are either very cautious... or you are a coward." If the player performs well in sneaking and/or combat, he will praise Snake for being a skilled warrior, and being well suited to this stealth mission.
 * Using his "blackout" technique, Psycho Mantis will change the player's screen to a black screen reading "HIDEO" in the top corner, as to replicate most standard television sets' VIDEO setting.
 * Campbell tells Snake that he must physically change the game controller's port on the PlayStation or GameCube, to prevent Psycho Mantis from "reading their mind." If the game is played on the PlayStation 3 or PSP, reassigning the controller works just fine.
 * In The Twin Snakes, Mantis will cause "sanity effects" during the battle by making the overhead camera tilt at an angle and cracking the screen if the player manages to make Meryl shoot at the screen.
 * Mei Ling will prompt the player to save after defeating Sniper Wolf the first time, saying that she has a bad feeling about what is about to happen (this is a reference to the torture sequence which happens after this fight).
 * When being tortured by Revolver Ocelot, he remarks that if the player uses a turbo controller's "autofire," he'll know and automatically kill Snake. If the player hasn't saved the game in a while, Ocelot will remark on Snake, saying "You really wanna go down that long road again?" He also mentions that "there are no continues, my friend." As such, this is the only part of the game where if Snake dies, the player cannot continue.
 * If playing with a DualShock controller (or, by having the vibration on in The Twin Snakes), Naomi will tell the player "to put the controller against (their) arm." She will then activate the controller's vibration functions, simulating a shiatsu massage. This occurs after the player has resisted two rounds of torture and is ready to escape. This is also referenced in Metal Gear Solid 4: Guns of the Patriots, when Psycho Mantis attempts to move the controller again but can't due to the SIXAXIS, a voiceover of Naomi will say "No more massages for you." However, if you are using the DualShock 3 controller with the PS3, Mantis will recognize the controller  and move it, causing it to vibrate and triumphantly shout out "Vibration is back!" But, Mantis, whether or not the controller is plugged in, will return to the netherworld regardless of the outcome.
 * While fighting the Hind D, Naomi and Campbell will advise Snake via Codec to use the television's stereo speakers to follow the direction of the Hind. However, if the audio is set to monaural, they will instead express their pity towards Snake for not owning a stereo TV set.
 * In The Twin Snakes, the screen will crack if Snake is killed while in first person view, a gameplay element carried over from Metal Gear Solid 2: Sons of Liberty.

Metal Gear: Ghost Babel

 * Before fighting Pyro Bison, Bison will tell Snake the number of sentries or bosses the player has killed up to that point.

Metal Gear Solid 2: Sons of Liberty

 * During Codec conversions in the Tanker chapter, if the player presses R1 to listen to Snake's positive thoughts, he will occasionally say "Hey, I'm the main character!" or "I'm the hero of this game!"
 * Whenever Snake or Raiden is killed in first person view, the screen cracks.
 * Similarly, if one is in first person view and attempts to blow up the sea lice via any type of explosives, while in first person, the sea lice will fly into and splatter all over the screen.
 * And if the player pulls a headshot, and then enemy is close enough, blood will splatter on the screen.
 * Snake tells Raiden that he needs to have the controller's vibration function on to use the AP Sensor, and Olga Gurlukovich tells him the same when speaking about the cell phone.
 * The entire Arsenal Gear sequence, after the virus is implanted onto GW, is a fourth wall break. The Colonel and Rosemary make cryptic messages, urging the player to turn off the console, saying lines from previous games - Metal Gear, Metal Gear 2, Metal Gear Solid, VR Missions and Ghost Babel, and famously spouting gibberish. At one point, he even specifically refers to Raiden's situation as a "role-playing game."
 * Snake, after meeting Raiden in the Arsenal Gear's bowels, remarks that he has "infinite ammo" while pointing to his bandana. This is a nod to Metal Gear Solid 's bandana. Once acquired, it gives the player infinite ammo for all weapons.
 * Just before Raiden throws away his dog tags at the end of the game, they display the information that the player entered at the beginning of the Plant chapter. This is often considered a metaphor for Raiden's refusal to remain a puppet and to start thinking for himself. Snake will also ask Raiden if he knows that person (i.e. the player), to which Raiden will reply "No."
 * In actuality, the whole message of Metal Gear Solid 2 's story breaks the fourth wall. Raiden's role in his "scripted" mission parallels the player's role in respect to the game. Snake directly refers to the fact that Raiden's only experience is in VR as "war as a video game", during which scenes from Metal Gear Solid: Special Missions are played. In addition, scenes from the game's menu and images such as that of the "Fission Mailed" screen are shown during the Colonel's explanation of the S3 system.
 * In the Snake Tales story External Gazer, Solidus talks to Snake about the Koppelthorn Engine and how it can let people control parallel universes, and vice versa. He asks Snake, "Have you ever felt like your body wasn't your own, like you took an unexpected action after the fact? Or you were able to do something you didn't think possible? That's because of interference from other universes. Perhaps the reason you were able to topple Shadow Moses is because of the helping hand from someone in another universe." This is a nod to the players of Metal Gear Solid, since they are the ones who control Snake.
 * A few times in the game, HIDEO 2 appears, either on a TV or a computer screen.
 * When Snake sends Otacon some random pictures during the Tanker Incident (instead of taking pictures of Metal Gear RAY), Otacon may say "Snake, this isn't a game we're playing here."

Metal Gear Solid 3: Snake Eater

 * Naked Snake describes wearing the Raikov mask as "nostalgic." This is because Raikov's appearance is based on Raiden, the protagonist of Metal Gear Solid 2. At the end of the conversation, Snake asks what he should do if he meets "that guy," with Zero responding that he should "beat the crap out of him."
 * During a conversation with The Boss, Snake mentions that he can't smell. It is actually the player that can not use their sense of smell to help play the game. The Boss then says that the player would "just have to rely on [their] instincts as a gamer." Master Miller says the same thing in Metal Gear Solid.
 * In the basement of the Granini Gorky Lab (heading towards Granin's office, not the prison), there are video game magazines scattered on the floor.
 * When EVA tells Snake about Raikov, Raikov is shown turning to the camera and smiling; an intentional nod at his likeness to Raiden, as well as a subtle reference to Raiden replacing Solid Snake in the previous game.
 * If Snake dies or kills Ocelot, Sokolov, or EVA, a Time Paradox screen is shown, as all four characters appear in games further on in the storyline. The future Colonel Campbell will also be heard questioning Snake (i.e. the player) over what he has done, and says that he's just created a Time Paradox.
 * In the introductory Codec conversation of the Snake vs. Monkey minigame, Solid Snake references stealth genre heroes Gabe Logan and Sam Fisher, of Syphon Filter and Splinter Cell fame, respectively. Snake also mentions Spike and Jimmy, two of the protagonists from the Ape Escape series. Campbell mentions other characters from Ape Escape, commenting that one of them is a friend of Otacon's.
 * Para-Medic uses some of the movies she mentions as real world metaphors for the player to not play the game too long or take it too seriously.
 * If The End dies of old age (should the player wait too long before resuming the game mid-battle, or change the PlayStation 2's internal clock), Snake will feel guilty for letting him down, since The End's dying wish was to fight him. Zero will also comment that Snake's mission is "not a game."
 * The Secret Theatre film, Metal Gear Raiden: Snake Eraser, is one big fourth wall break.
 * At the beginning of the film, Raiden comments on killing Naked Snake and take his position in the "Main Character" chair.
 * Whenever Raiden time travels and something bad happens, Campbell can be heard saying that he created a Time Paradox.
 * When Raiden returned to his original time, Rosemary tells him that the past can't be changed and that they can only change the future. Raiden then starts to say something about Metal Gear Solid 4, but Rose reassures him, telling him "There's going to be a 5, right?"

Metal Gear Solid: Portable Ops

 * In an optional radio call with Sigint, Snake will make references about "changes in equipment" where things have become lighter and more compact overall, the controls are completely different, and yet he can now "take the equipment outside" a direct reference to Metal Gear Solid being placed onto the PSP.

Metal Gear Solid Mobile

 * When the AI starts crashing due to Otacon's hacking, Commander tells the player to turn off their cellphone.

Metal Gear Solid 4: Guns of the Patriots

 * Old Snake uses a DualShock 3 controller to operate the Metal Gear Mk. II or III. This is also present in the game's instruction manual, where an artwork of Snake controlling the miniature Metal Gear with the same controller, along with instructions regarding the control scheme beneath the artwork, are all shown.
 * During Drebin's introduction, he will wave his title card away with his handkerchief.
 * When Snake enters the Blast Furnace in Shadow Moses, Otacon contacts him by Codec and tells him to change game discs (this is where the disc change occurs in Metal Gear Solid). He quickly, however, realizes that a "Dual-layered" disc eliminates the need to do so, complementing the PlayStation 3 hardware, before Snake tells him to "get a grip."
 * The entire Screaming Mantis fight is used to play on the player's memory of the Psycho Mantis fight. At one point, Mantis will change the screen to read "HIDEO 2", but if the player changes the controller port, Snake will still be unable to move and Otacon will tell him that tactic "won't work this time." Colonel Campbell suggests this technique if the player contacts Rosemary on the codec, and Rosemary will point out the flaw in his logic. Another plan suggested by Campbell is shooting off the leather straps from the Psycho Mantis bust, another tactic from the earlier game, but Snake will point out that there is no bust in this area. And if the player actually does assign the controller to something other than "1" Snake will say that he can't move and Otacon will ask if he assigned the controller to something other than one. He'll also say that the controller has to be on "1" or Snake won't be able to move. Also, in a very rare case, Mantis may "restart" the game, in which the Konami logo will appear, followed by a backwards Kojima Productions logo. After this, the player can resume as though nothing happened.
 * After defeating Screaming Mantis, Psycho Mantis will appear and repeat his psychic and telekinesis performance from Metal Gear Solid. However, due to the hardware, he is unable to read the memory card, and his failed attempt to vibrate the SIXAXIS controller prompts an annoyed outburst (Naomi is heard saying "No more massages for you" referencing another scene in Metal Gear Solid).
 * If the player uses a DualShock 3 controller for the above sequence, Mantis will successfully move the controller and gleefully declare that "Vibration is back!"
 * If the player calls Rosemary after being killed and selecting the continue option, Snake will occasionally start talking about dreams of dying or that he's "died recently."
 * In a Codec conversation, Otacon asks if Vamp is immortal, to which Snake replies, "Not a chance. This is the real world, not some fantasy game."
 * If Snake dies during the fight against Liquid Ocelot, the "Exit" option becomes "Exist." If "Exist" is chosen, Liquid will reply, "Snake! It's not over yet!", a recurring phrase throughout the series. "Exist" will also change back to "Exit" and the marker will also go back to the default "Continue." The "Continue" will also shrink.
 * In a conversation with Naomi as she describes the SOP system, she mentions that the PMC soldier's battle experience "was just a game to them." During this conversation, the covers of Metal Gear, Metal Gear 2: Solid Snake, Metal Gear Solid, Metal Gear Solid: Integral, Metal Gear Solid 2: Sons of Liberty, Metal Gear Solid 2: Substance, Metal Gear Solid 3: Snake Eater, Metal Gear Solid 3: Subsistence, and Metal Gear Solid: Portable Ops flash through before stopping at Metal Gear Solid 4: Guns of the Patriots (depicted as a video), with two blank squares in front of Metal Gear Solid 4 labeled "Under Construction", which was likely talking about Metal Gear Solid: Peace Walker and Metal Gear Solid: Rising (now known as Metal Gear Rising: Revengeance).
 * When Snake enters the house after following the resistance member in Act 3, the player can see posters referencing Metal Gear Solid, Metal Gear Solid 2, Metal Gear Solid 3, and Metal Gear Solid: Portable Ops. These posters are artwork done by Noriyoshi Ohrai.
 * While Snake is in Shadow Moses, if the player moves the camera so that it's above Snake instead of behind him, Snake will say "Overhead view... Just like old times. Now you're talking! Overhead view! That's more like it!" This is also a reference back to Metal Gear Solid where the whole game is played in overhead view.
 * If the player dies while fighting Screaming Mantis, strings will appear on Snake, thus signifying the he's a "puppet of the player."
 * Sometimes when attacking an enemy and wounding it, blood will splatter all over the screen, similar to what happens in Metal Gear Solid 2.

Super Smash Bros. Brawl

 * During a Codec conversation about Pit, Otacon mentions how Snake knows all about "Game Overs."
 * During the Subspace Emissary storyline, Snake says "Kept ya waiting, huh?", both breaking the cinematics' tradition of refraining from spoken dialogue and directly addressing the players. This is also a reference to Hideo Kojima wanting Snake to appear in the previous game, Super Smash Bros. Melee, which didn't happen due to time constraints. It could also be a nod to a cutscene, shown much earlier, where it simply shows Snake in a box.
 * If the player contacts Otacon while fighting Sonic, Snake will say that he doesn't like Sonic for some reason. When Otacon questions him about it, he states that "something about [Sonic] just rubs me the wrong way...". This could be a reference to the fact that in real life, hedgehogs eat snakes. This could also refer to the fact that Snake was supposed to be the only third party character in Brawl before Sonic was announced to appear as a third party character. The most likely reason for this comment is the fact that the Japanese voice actor for Snake, Akio Otsuka, is the son of Eggman's voice actor, Chikao Otsuka, Eggman being Sonic's nemesis.

Metal Gear Rising: Revengeance

 * Sometimes when attacking an enemy and wounding it, blood will splatter all over the screen, similar to what happens in Metal Gear Solid 2.
 * In Metal Gear Rising 's first trailer, Raiden says "Let's have some fun", which is partially directed at the player.
 * During gameplay, the combat manual will display the gameplay controls in different situations, like the Slider segment of Sundowner's boss battle. This is a fourth wall break in itself, as the game's HUD is Raiden's AR display.
 * In the lower right hand section of Raiden's HUD the words "METAL GEAR SOLID TV" can be seen.
 * During a codec conversation, Boris tells Raiden his mission is "no game."
 * At the end of the Senator Armstrong battle Raiden subtly breaks the fourth wall when he says "We're done here" since Armstrong is the final boss and the player had finally defeated him.
 * At one point in Samuel Rodrigues' DLC, he asks why the Denver sewers "look so familiar."

Metal Gear Solid: Ground Zeroes

 * As Big Boss takes his night vision googles off, when the camera zooms in onto his face he says "Kept you waiting huh" which is also the same lines Solid Snake says to Roy Campbell.
 * After Kaz Miller learns that Big Boss is in a coma, Kaz asks "What about him?" and then the camera still focusing on Kaz zooms to the direction Kaz is looking. Kojima revealed that it was him Kaz was refering to.

Metal Gear Solid V: The Phantom Pain

 * After Big Boss gets up from his coma a man called Ishmael gives him an injection saying "Nothing like a little digoxin to get you back in the game."
 * As Big Boss gets the ability to walk again he walks past a Ground Zeroes poster of himself.