-> ''"Blink your eyes''
-> ''Once for yes''
-> ''Two for no..."''
-->-- '''Music/{{Radiohead}}''', "Bodysnatchers"

A character is only able to communicate through a limited set of responses, but tries to convey a lot more information than their medium provides. The title refers to the most extreme version, where the character has only ''one'' possible response they can give.

In one standard version of this, the "character" is a spirit at a (generally faked) seance, and all they can do is rap (usually because it's easy for whoever's faking the seance to make a rapping sound discreetly under the table). They then end up rapping once for yes, twice for no, and then spelling out a message by having the participants in the seance run through the alphabet, to be stopped by a rap when they reach the next letter in the message.

A common joke is for two raps to be misinterpreted as "yes, yes". Another (often in the seance variant) is for a character to say "Is there anyone there? Knock once for yes, [[FridgeLogic twice for no!]]"

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!!Examples:

[[foldercontrol]]

[[folder: Advertising ]]

* There's a radio commercial for Geico insurance which involves "the money you could be saving if you switch to Geico", a stack of money with googly eyes. The announcer asks the money to blink once for yes, twice for no, but then he keeps blinking himself and can't tell if the moneypile has been blinking.

[[/folder]]

[[folder: Film ]]

* Bumblebee in the ''Film/{{Transformers}}'' films can only communicate by tuning his radio to different stations.
* ''Blithe Spirit'' ([[BlitheSpirit no relation]]) has a seance that uses this.
* In ''Explorers'', a group of kids somehow learn to use their home computer to produce and control a spherical forcefield of arbitrary size and position, eventually using it to build a spaceship. The aliens they meet at the end of the film speak entirely in reproductions of pop culture from Earth's TV broadcasts.
* In ''Dark Passage'' (1947), fugitive Vincent Parry has just gotten a face-lift from plastic surgeon Dr. Walter Coley. After the operation, Parry's face is bandaged and the doctor tells him not to move his mouth until he is completely healed:
-->"Now...I'm going to ask you some questions. If the answer is 'yes', just blink."
* Bit in ''Film/{{Tron}}'' can only say "yes" or "no" (see also Truth in Television), but can also be more emphatic by repeating itself ("yesyesyesyes" or "[[OhCrap nonononono]]").
* ''Film/{{Anchorman}}'': "Baxter, is that you? BAXTER! Bark twice if you're in Milwaukee!"
* ''Film/{{Hannibal}}'' Lecter forces a BoundAndGagged victim to communicate with him this way, by blinking his eyes.
* ''Film/BlackSunday'' has Kabakov interogating a man who rented a wooden boat to an American Terrorist, and Kabakov wants him to tell who it was. So he hides on the man's boat in the marina, and when he gets on his boat, Kabakov knocks him down and asks him at gunpoint whether he'll tell him want he wants to know, "Blink for yes, die for no." The man blinks.

[[/folder]]

[[folder: Literature ]]

* ''Literature/ToSayNothingOfTheDog'' has a faked seance with rapping. [[HilarityEnsues Hilariously,]] there are two different sets of people trying to fake it, with very different motivations for what they want the "ghost" to be saying.
* In the LordPeterWimsey novel ''Strong Poison'', Miss Climpson fakes a seance, as an excuse to search the house of a dying woman for a will that Lord Peter suspects will contain incriminating evidence.
* One of the [[PlayWithinAPlay stories within the story]] in Creator/GeneWolfe's ''Literature/BookOfTheNewSun'' is told by a man who only ever speaks in political slogans. Another woman translates these into eloquent prose, rendering the story intelligible (and moving).
* In ''Literature/LifeTheUniverseAndEverything'', Eddie the computer is gagged and Zaphod tells him to make "mmmm" once for yes and twice for no. Leading to a funny dialogue: "Is it dangerous?" - "Mmmm." - "You didn't just say 'Mmmm' twice?" - "Mmmm mmm." - "Hmmmm."
* During ''[[XWingSeries Wraith Squadron]]'', Gammorrean pilot Piggy's translator breaks, and his grunts aren't understandable, so when asking if he's okay, his squadronmates resort to this.
* Fox in MatthewReilly's Shane Schofield trilogy had to use this technique twice: by tapping her wrist mike when she couldn't move, and coughing when she was under guard. Apparently "one for no, two for yes" is more dramatic, especially if the hero is going to ask "Are you alright?".
* The ''IncarnationsOfImmortality'' series has Sning, the magic snake ring that answers any question the wearer asks of it by squeezing his (or her) finger: one squeeze for yes, two for no, three to indicate that a yes-or-no answer cannot be given.
* Spoofed in ''Discworld/ReaperMan''. During a seance, Mrs. Cake's spirit guide One Man Bucket gets a bit confused about which is which. Also, he's perfectly capable of speech, and only has to knock on tables because Mrs. Cake's clients [[TheCoconutEffect expect that sort of thing]] in a seance.
* Noirtier de Villefort in ''Literature/TheCountOfMonteCristo'' is completely paralyzed except for his eyes. He communicates by a system of blinks, including two agreed-upon signals meaning yes and no.
* In ''Literature/IWillFearNoEvil'', a doctor uses the alphabet system (with vocal noises by a patient with a mouth full of medical equipment) to communicate with the protagonist immediately post-surgery.
* Creator/DickKingSmith's book ''Ace'' is about a pig named Ace who has the unique natural talent of understanding everything humans say, and works out a way of communicating with farmer Ted Tubbs by grunting once for "no" and twice for "yes." He briefly ponders expanding on it by devising specific meanings for three grunts, four grunts and so on, but ultimately decides this will get too complicated for them both.
* In ''Small Favour'', [[Literature/TheDresdenFiles Harry Dresden]] mocks this idea when his EvilDetectingDog seems unsure if something's wrong or not. "You know, Franchise/{{Lassie}} would have given a clear, concise message; one bark for [[ProfessionalKiller Gruffs,]] two for Nickelheads."
** He does it when comunicating with an inch-tall wyldfae named Elidee. Blinking faelight is the only effect she can produce that Harry can percieve.
* Creator/EphraimKishon's buddy Jossele / Erwinke once invents a code like this, when his boss forbids making private calls during the work: He and his co-worker will let the phone ring X times without taking the call. 43 times means "have you seen the latest Creator/WoodyAllen flick already?" 46 times means "I did, but it wasn't that special", and so on.
* In ''Literature/ASongOfIceAndFire'', Night's Watch scouts use a horn to signal one of three events: one blast for returning brothers, two for wildlings, and three for Others. Whenever the first blast is heard, the men wait with bated breath for the possibility of a second one turning good news to bad.

[[/folder]]

[[folder: Live Action TV ]]

* ''Superior Court'': An episode of this 1980s courtroom drama had an episode where a witness, rendered a vegetable after a game of Russian roulette, testify at a murder trial by answering yes/no questions through blinking. His testimony helps convict the defendant.
* Captain Pike, in the ''Series/StarTrekTheOriginalSeries'' episode "The Menagerie," can only beep once for yes and twice for no. At one point he's found repeating "no" over and over again to warn of something he has learned.
* The nebula alien in an episode of ''Series/StarTrekVoyager'' communicates with the crew via the limited phrase book of the ship computer.
* In the ''Series/StarTrekTheNextGeneration'' episode "Darmok", an alien tries to communicate with Picard using a language comprised solely of metaphors. In practice (and to keep the audience from getting confused), this involves trying to communicate using only a handful of phrases over and over.
* In one episode of ''Series/{{House}}'', the medical team connects a man with locked-in syndrome to a computer controlled by his brainwaves, allowing him to move a cursor to yes, no, etc. And that's after he couldn't blink anymore.
* ''LawAndOrderSpecialVictimsUnit'':
** In one episode, a brain dead patient's therapist gets killed. They suspect the vegetable's husband, who was trying some sort of fraud to profit off the both of them, or something. To get him to confess, they have the dead therapist's assistant set up feedback from the vegetable, using set up "Yes" and "No" questions and detecting brainwave spikes for a "Yes" if she doesn't look at the signs. [[spoiler:Subverted in that it really doesn't work - they're relying solely on the perp's guilty conscience, since the therapist's assistant explicitly states this won't work to the detectives.]]
** This also shows up in an episode concerning a multiple sclerosis patient who is reduced to blinking twice for yes and once (or crying) for no. Most of the latter half of the story is largely concentrated on the detectives trying to get her to use her fingers to point at the guilty suspect, as this trope is too weak to use in a court case.
* The early-90's UK kids' show ''Woof!'' has this when the main character becomes a dog.
* An episode of ''Theatre/TheOddCouple'' has a "seance", where Oscar plays a joke on Felix by doing the knocks (in another room), pretending to be the ghost of the previous tenant.
* ''Series/MontyPythonsFlyingCircus''. A coffin is brought into court. After the prosecutor asks the dead man inside it a question, a "bang" is heard coming from it.
-->'''Judge''': What was that knock?
-->'''Prosecutor''': It means "yes" m'lud. One knock for "yes," and two knocks for "no."
** Eventually the prosecutor asks a question; getting no answer, he looks inside the coffin, drops the lid, and says "No further questions, m'lud."
** At the end of ''[[Series/MontyPythonsFlyingCircus Monty Python Live in Aspen (1998)]]'', Graham Chapman's ashes use this method of communication to bring Film/MontyPythonsTheMeaningOfLife from beyond the grave. The urn then taps out the melody for "Always Look on the Bright Side of Life."
* Crichton invokes this in an episode of ''Series/{{Farscape}}'' in order to communicate with a DRD. He even calls it the ''Star Trek'' method.
* This is used in ''Series/{{Community}}'' with Abed and a Secret Service agent [[StalkerWithACrush keeping tabs on him]], reversed so two car honks is yes.
* Jack the dog in ''TalesOfTheGoldMonkey:'' barks once for "no," and twice for "yes." And he's always right.
* ''Series/BreakingBad'': Hector "Tio" Salamanca is confined to a wheelchair and unable to speak in his old age (possibly from a stroke). He presses a bell attached to his wheelchair arm once for "yes" and does not press it for "no." This unusual method of communication is used for several humorous scenes as he tries to convey his meaning to other characters, but is sometimes used more dramatically, as he reveals he knows more than his senile appearance lets on.
** Most dramatically in the season 4 finale, when [[spoiler: Walt connects a bomb to the bell. When [[BigBad Gustavo Fring]] arrives to kill Hector with a lethal injection, Hector activates the bomb by rapidly pressing his bell, instantly killing himself and [[ScaryBlackMan Tyrus]] and fatally blowing half of Gus's face off]].
* The pilot of {{CSI NY}} had Mac using this with a woman suffering from locked in syndrome. Unfortunately, she had a stroke before he could finish questioning her. This was an inversion of the standard code as Mac choose to have two blinks mean "yes" and one mean "no".
* One episode of ''Series/MurdochMysteries'' features a man suffering from aphasia who communicated with ringing a bell. Once for yes, twice for no. [[spoiler: He was actually faking this medical condition of his.]]
* ''PersonOfInterest''. Finch is shown communicating with the Machine in its early days via this method, using the vibration-tone setting on his mobile.
* In the ''Series/{{Supernatural}}'' episode [[Recap/SupernaturalS09E01IThinkImGonnaLikeItHere "I Think I'm Gonna Like It Here" (S09, Ep01)]], Dean has Crowley locked in the trunk of the Impala. He asks Crowley to knock once for yes and two for no, and then asks Crowley if he is alive.

[[/folder]]

[[folder: Music ]]

* "Knock three times on the ceiling if you want me/ Twice on the pipe if the answer is no..." - the classic [[TheSixties late 60s hit]] "Knock Three Times" by Tony Orlando and Dawn, prevents the "yes yes" dilema by using different objects for yes and no.
* "One blink for yes, two blinks for no / Sweet dreams, sweet cheeks, we leave alone" - ''Sweet Dreams, Sweet Cheeks'' by Music/LosCampesinos!. Implied to be a girl in a coma or paralytic state being asked if she wants euthanasia.

[[/folder]]

[[folder: Radio ]]

* Late 70s [[TheBBC BBC]] {{Radio}} sketch series ''TheBurkissWay'' used this once. It went something like:
-->'''Interviewer''': Tonight we have in the studio the late Dr. Leibnitz Ectoplasm. Dr. Ectoplasm, do you believe in life after death? (Long pause) ...One tap for "yes," two taps for "no."
--> (Two taps)
--> '''Interviewer''': So there we have it - "Yes, yes," says Dr. Ectoplasm.

[[/folder]]

[[folder: Stand Up Comedy ]]

* Creator/JasperCarrott does the seance joke version of the trope ("Is there anybody there? Knock once for yes, twice for no!")

[[/folder]]

[[folder: Video Games ]]

* The Superintendent Municipal AI in ''VideoGame/{{Halo 3}}: ODST'' can only communicate via pre-recorded audio city notices and traffic signs. For example, when attempting to ask marines to not blow up a bridge, it asks them to 'Keep It Clean, Respect Public Property'. When faced with the eventuality that the Covenant would soon be accessing it's datacenter, the AI releases the bridge controls and ironically responds 'Bridge Toll Accepted, Have a Pleasant Trip.'
* In ''VideoGame/KnightsOfTheOldRepublic'', you can suggest for Bastila to help you with the KarmaMeter by blinking once for Light Side, twice for Dark Side. She's not amused.

[[/folder]]

[[folder: Web Comics ]]

* ''Webcomic/DarthsAndDroids'' has an [[http://darthsanddroids.net/episodes/0081.html explanation for R2-D2's sounds]].
* ''Webcomic/SluggyFreelance'' referenced the ''Franchise/StarTrek'' example by having Torg's idea of helping, when he had accidentally transformed Zoe into a camel, be to build her a machine with 'yes' and 'no' lights.
* ''Webcomic/TheWotch'': [[http://www.thewotch.com/?date=2005-08-01 Will you or will you not lead us to the Wotch? Nod for "yes", shake your head for "please, cut my leg off!"]]

[[/folder]]

[[folder: Web Original ]]

* Silent Pete from the Machinima ''PreGame Lobby'' only communicates via music clips.
* [[http://bash.org/?10958 Communicating in binary.]]
* ''Franchise/{{Neopets}}'': "Clop" is an unspeaking prisoner who communicates only by knocking his hoof on the floor. One is yes, two is no, three means he's hungry... Too bad nobody knows what four and five mean.
* In ''Literature/{{Worm}}'', in [[http://parahumans.wordpress.com/2012/08/25/snare-13-09/ Chapter 13.9]], Skitter has a conversation this way with [[spoiler:Bonesaw]].

[[/folder]]

[[folder: Western Animation ]]

* Parodied in ''WesternAnimation/{{Futurama}}'' where [[GeneralFailure Zapp Brannigan]] tells Fry in a Captain Pike-like device[[note]]actually a machine for testifying; yes, it makes no sense, but this is Zapp we're talking about.[[/note]] to beep once for guilty, twice for not guilty. After Fry beeps twice, Zapp concludes, "Double yes! Guilty!"
* Similar to the ''WesternAnimation/{{Futurama}}'' example, in a ''WesternAnimation/SouthPark'' episode an ex-teacher could only move through a machine which could also beep (everybody thought she was giving everybody the silent treatment when the batteries died), and is asked by the police officer whether a suspect was involved in a crime she witnessed, he interprets her bleeps as "yes, yes!"
** The commentary specifically says that they just wanted to make the "Yes, yes" joke with her.
* In ''WesternAnimation/TheSimpsons'' Bart is diving looking for a treasure and arranging to alert Abe if he needs more oxygen or needs to be raised... by pulling a rope 63 times if he's out of air and 64 if he finds the treasure.
-->'''Abe:''' 61... 62... 63... Oh no! 63! He's out of air! I've sent my only grandson to a watery graaaav... 64! He's found the treasure! I'm rich!
** In another episode ("The Last Temptation of Krust"), Krusty wakes up in Bart's room after a drinking binge, and with his weakened state he tells Bart that they should devise a code of eyeblinks to communicate. Bart immediately starts winking out a response, to which Krusty protests, "Not you!"
* This happens in ''IvorTheEngine'' when his crew try to communicate with him early on. Except there they tell him "One for no, two for yes."
* In ''SonicUnderground'' Manic uses this to communicate with Knuckles' pet dinosaur. "One bark means yes, two barks means no."
* The ''WesternAnimation/TaleSpin'' episode "All's Whale That Ends Whale" features a trained whale. When Baloo and Kit disocver that the whale's sleazy trainer has been mistreating him, the trainer alters the whale's responses to keep from losing his meal ticket.

[[/folder]]

[[folder: Truth In Television ]]

* StephenHawking has lost almost all control of his body, and can only communicate with a computer through feeble squeezes.
* Binary Code (computer language) is made up of an extremely complex combination of ones for "Yes" and zeroes for "No", which proves that any concept able to be expressed as a word can be boiled down to those two utterances.
* Jean-Dominique Bauby (author of TheDivingBellAndTheButterfly) suffered a massive stroke and was left with control over one eye. At first he could only answer "yes" or "no" questions but his doctors devised a new system of reading out letters. This meant he was able to write his novel one blink at a time.
* The legendary "one if by land, two if by sea" quote from the American Revolution is one of the most famous historical examples, where a guy is supposed to hold up one lantern if the British are approaching by land, and two if they are coming via river (sea).
* An atypical example: in Japanese, "un" means agree while "uun" means disagree.
* May be used in trying to communicate with paralyzed persons who can't otherwise speak or write, ie those with 'locked in' syndrome, where only the eyes can move.
* American prisoners during the VietnamWar would devise codes they could use to send messages back and forth by knocking on the wall between their cells. Since they [[ParanoiaFuel couldn't actually tell]] if the guy in the next cell was a fellow prisoner or a guard trying to trick them, they would sometimes resort to tapping out "ShaveAndAHaircut" to see if their neighbor [[TrustPassword would knock twice for "two bits" or not]].
* Ricardo Woods shot David Chandler in the face and neck in Cincinnati in 2010, leaving him paralyzed from the neck down, on a ventilator, and only able to communicate by blinking his eyes. Before Chandler died, he blinked his eyes three times for "yes" when police showed him a photo of Woods and asked if that was the man who shot him. In June 2013, Woods was sentenced to 36 years to life - a year less than the maximum - for the murder and other charges.
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