Sherlock Holmes: To the curious incident of the dog in the night-time.
Inspector Gregory: The dog did nothing in the night-time.
Sherlock Holmes: That was the curious incident.
Sometimes the absence of a thing is a vital clue. For example, the absence of fingerprints on an often-used item makes it clear that the item was cleaned. A tool missing from a set could well be the murder weapon. And, as indicated in the page quote, a dog failing to bark at an apparently unknown intruder suggests that the dog was probably familiar with whoever it was.
This is, in fact, one of the harder aspects of real police investigations. The lack of something is easy to miss. However, you have to be careful. The lack of gunshot residue on a person's clothes, for example, does not mean that there was not a gun fired, it means that there is no gunpowder residue to find ("The absence of evidence is evidence of absence, not proof of absence"). Lack of such residue on the glove that an eyewitness saw the shooter use and then dump that is immediately picked up by the police might show that the event was staged, however (as the gloves would have residue and there is no way it might have been removed). Also, in Real Life, people firing a modern semiautomatic pistol often don't acquire any gunpowder residue on their hands; so while the presence of gunpowder residue may be evidence of guilt (weak in itself the residue could as easily have been picked up at a shooting range), its absence does not exclude a suspect.
Can lead to a Conviction by Contradiction situation if poorly handled.
Compare I Never Said It Was Poison, where someone incriminates themselves by mentioning details which were withheld from the public, and It's Quiet... Too Quiet for the audio-exclusive version of this. Contrast Not Proven, where the police or the prosecution don't have enough evidence to convict a criminal.
- Often used in Detective Conan:
- The daughter of a wealthy businessman has been kidnapped and Conan figures out who the kidnapper is when he remembers that no one reported hearing the sounds of dogs barking the previous night. (For clarification, the butler who claimed to have witnessed the kidnapping said that the kidnapper climbed down a tree, but the businessman's dogs routinely barked at anyone who got near the tree.)
- A man suspected to be the one who had been randomly attacking women with a mallet is found strangled in his own apartment...except Conan can't find any underwear, shoes, or toiletry there. He quickly realizes that the apartment belongs to someone else, who removed those items to hide the fact that she, a woman, lived there and was the true culprit.
- In Monster, Johan's crime scenes are "devoid of feeling" — the kills are executed as coldly and methodically as household chores. In one arc, this enables Runge to determine that a certain murder was committed by a copy-cat and not Johan — blood spatter clearly shows a man had been slouched in front of a mirror, but his body is found several feet away because the killer hesitated upon seeing himself in said mirror. Johan would have killed the man without a second thought, but the real killer — the man's nephew — was shocked to see himself in the process of killing.
- In the first Judge Dredd comic in Hondo-City, the Hondo-City Judge works out that the assassin he is chasing is a robot because there is no rollmat, no food, no toothpaste, etc., in his apartment.
- This was, oddly enough, used to discover Superman's secret identity back in the Silver Age of comics. Superman has since started filling his bathroom with all the things needed for daily life, and putting medicines in his locker.
- It's used in Superman: Earth One, when Lois is doing some digging into Clark Kent's life. Because he spent his childhood trying not to stand out in any way at all, not making any friends and just performing averagely at school, it tips Lois off that he's hiding something.
- In the DC one-off "World Without Grownups" (a prelude to Young Justice), it appears as though all the children in the world have disappeared. However, Batman deduces that the ADULTS were the ones who were transplanted to a parallel earth when he notices that none of his bat-gear has any dust on it (and then proceeds to carbon date everything he can find to back up his hypothesis).
- In "Fall Guy for Murder" from Crime SuspenStories #18, a man hires a detective to find his wife who he claims took everything she had and ran out on him. The gumshoe immediately becomes suspicious when he sees that literally every last thing she had ever owned was missing; every piece of clothing, every single pair of shoes, every last hat, all of her luggage, etc. As he notes, a lady running away from her husband on the quick would leave behind something she wouldn't bother taking. It turns out to be a set-up.
- In The Bourne Ultimatum when the CIA is looking for whoever leaked Blackbriar to the media, their initial response is to check for whoever's cell phone was in the same location as the meeting place. Pamela Landy notes that what they should be doing is checking who has their cell phones turned off, as no employee of the CIA would be stupid enough to meet a journalist with their phone on but that it would be odd for a ranking officer to be out of contact for that long.
- In Memento, Leonard shows Natalie a binder of documents he has pertaining to the attack on and murder of his wife; she comments that it seems awfully incomplete for how long his investigation is going. Then you find out that Leonard destroyed several pages before the beginning of the film's events, intentionally creating holes that he could exploit to continue seeking his aimless revenge.
- One of the final reveals in Rashomon is that the woodcutter, who at that point was the only person the viewer would be inclined to believe entirely, stole a valuable dagger mentioned by all the other witnesses, but the object was never mentioned by him.
- In Tomorrow Never Dies, Henry Gupta sees through James Bond's cover story of being a banker and deduces he's a government agent, based on the lack of any blemishes on Bond's falsified records.
Gupta: I call it "Gupta's Law of Convenient Anomalies" - if it looks Too Good to Be True, it probably is.
- In The Usual Suspects, the absence of any cocaine in the cargo ship is the first sign that the attack isn't what it first seems.
- In Sherlock Holmes: A Game of Shadows during the climax both Watson and Simza have to find Simza's brother before he can go through with an assassination plot, while Sherlock is out of the room. Deducing that the assassin is going to be one of the guests and will be in disguise they cannot rely on Simza to recognize him. Watson correctly states that they shouldn't be looking for any telltale markings that Simza will recognize, but rather they should be looking for something that someone in the assassin's position wouldn't have or be unable to produce: spontaneous reaction. Sherlock then reveals both he and Watson's mindset, the assassin is currently acting as an ambassador therefore he is so caught up in his performance to keep up his charade that he cannot accommodate for regular actions or reactions namely surprise. Watson then causes a commotion to find the assassin, whose lack of reaction towards the event makes him stick out of the crowd and is then prevented from carrying out the plot.
- Peppermint: The police and FBI are clued in to the heroine's whereabouts by looking at crime maps, and finding an area in a run-down section of town that is suspiciously free of crime.
- In Aquarium, a superior asks Suvorov whether he knows what a certain section of the intelligence department is dealing with. Turns out he does — since he never received any data from them, the obvious conclusion is that these are units which only operate during the war. Combined with the available data about the section's officers, who are all very tall, that means these are recon and sabotage units. Well, the proper name for them is Spetsnaz, but of course that cannot be obtained by deduction.
- In Artemis Fowl: The Opal Deception, Opal Koboi has a specially constructed shuttle made entirely of "stealth ore" that is supposed to be almost impossible to detect with most conventional technology, in order to evade the authorities. Artemis gets around this by modifying the scanners on his own shuttle to detect unnatural absences of common elements... and very quickly finds what appears to be a shuttle-sized vacuum at the place where Opal is hiding.
- This trope is referenced in the first novel of the Bernard Samson series. While Bernard is in custody of an East German intelligence officer, they discuss the story of Silver Blaze. Bernard then points out the equally curious omission of any attempt at a proper interrogation. The reason for it is that the officer's boss is Bernard's wife.
- In the Death Note novel Another Note, this was the basis for all of Beyond Birthday's clues: "Something that should be there, but isn't."
- Parodied in the Discworld City Watch books, where Vimes notes how hard it is to find something missing because said thing is, by definition, not there.
- Dragonriders of Pern: In Dragondrums, Piemur is sent to the Drum towers to learn drumming while his voice is changing from puberty. During his time there, he proves skilled and adept at learning the drumming codes enough to piss off the boys who have been there much longer. So, they start bullying him in progressively harsh ways. The final attack on Piemur is when they place grease on some steps they know he would be rushing on to deliver the message. After his hard slip and cracking his head on the stone floor, the culprits clean off the grease. While one of Piemur's seniors doesn't believe him about the greased steps noting they were perfectly clean, the responsible one realizes that the steps in question were too clean. The other steps in that staircase were dirty compared to these few ones.
- The Dresden Files:
- In Fool Moon, Johnny Marcone knows that Harry has snuck onto his estate even though (or because) he didn't see him do it: one of his security cameras went on the fritz and he says, "Such malfunctions and Mr. Dresden tend to go together."
- In Small Favor, Michael suspects that Harry is under some form of magical influence because throughout the whole novel up to that point Harry has not once used the fire magic that is normally his go-to spell, and the blasting rod he uses to focus his fire magic is nowhere to be found. When Harry confronts Michael about his suspicions, Michael is able to prove to Harry that something is wrong by quietly asking where his blasting rod is in fact Harry is under a spell by the Queen of the Unseelie Court to prevent him from using fire magic, and only when Michael brings it to his attention does he realize (along with most readers) that his blasting rod is missing and that he hasn't so much as thought about it or fire magic throughout the novel up to that point.
- Honor Harrington: In Echoes of Honor, a State Sec general figures out that the prisoners have taken over the prison because the warden failed to send his next chess-by-mail move in the mail delivered by a courier ship.
- Subverted in an I, Robot story called, appropriately enough, "Evidence". Someone arrives at US Robotics claiming that Presidential candidate Stephen Byerley is a robot because he never eats or sleeps. Byerley points out that even if the man's been spying on him, all he knows is that he wasn't eating or sleeping then.
- The Lord Peter Wimsey mystery The Five Red Herrings turns on the absence of a tube of white paint from the crime scene.
- Miss Marple: The maid in The Moving Finger looks vainly through the window all afternoon for her boyfriend, but sees nobody, not even a postman meaning that the poison pen letter occasioning her employer's wife's "suicide" that day did not come through the mailbox.
- This trope was crucial to solving the murder at the heart of the James Herbert novel Nobody True, which initially appeared to be the work of a Serial Killer. It turns out that the police had deliberately left out certain key details about what said killer did to the bodies of its victims when talking to the media in order to make a copycat killer easy to spot. This managed to even fool the ghost of this particular victim.
- Sherlock Holmes has supplied us with several examples:
- In the story "Silver Blaze" that gives us the page quote, Holmes points out the vital non-clue of a dog failing to react to a mysterious visitor... when a guard dog doesn't bark at an intruder it generally means it's someone he doesn't think is an intruder at all.
- The absence of certain valuable deeds is a vital clue in "The Norwood Builder".
- In the Sword of Truth novel Chainfire, after the eponymous spell has made everyone forget that Kahlan ever existed, Richard tries to use this to convince everyone else that she has. He points to where he says he, Kahlan, and Cara had been walking, and notes that there were no footprints between his and Cara's, which were several feet apart. He tells his companions that this means someone erased Kahlan's footprints. Nobody believes him since, as mentioned, everyone is sure that she never existed in the first place.
- Terra Ignota: Inverted. There is some vague, contradictory evidence that the Utopians were behind the theft of the Seven-Ten List in an attempt to discredit the Humanists and their car system in favor of the Utopians' own car system. When the world leaders ask Mycroft what he thinks, he points out that if the Utopians were involved, they would have done it so perfectly that no one would have suspected them for a second.
- In one of the Union Club Mysteries by Isaac Asimov, Griswold points out that the female suspect they are looking for (who has been shown to be fanatical about stockpiling supplies she will need) must be post-menopausal as there were no products for dealing with menstruation in her apartment.
- Whateley Universe: How Tansy manages to find Kayda under an invisibility charm in as said in The Bear, the Bitch, and Everything (Part 3):
Since she was using her invisibility charm to hide from everyone, I attuned myself to the emotional flow of the school and went looking for a void."
- In one episode of The Andy Griffith Show, one resident of Mayberry reported that his cow was stolen. An expert criminal forensic scientist comes out and wows everyone but Andy with his scientific knowledge. As they analyze the crime scene they identify three different sets of boot prints which the expert says belong to three different suspects. Andy is the only one to notice something important which is missing, the cow's footprints.
- In an episode of City Homicide, the body of Matt's mother is found on a construction site, fourteen years after she disappeared while buying balsamic vinegar from a local shop. When the team realize she was found without said balsamic vinegar, they conclude that the shopkeepers lied about her leaving the shop.
- Columbo: The episode called "The Most Crucial Game" has the culprit caught when Columbo found that the phone call the killer claimed to have made at 2:29 pm in his stadium box (and recorded by a bug on the line) lacked the sound of the half-hour chime of the anniversary clock in the box.
- On CSI, when a serial killer strikes Las Vegas, killing women with towels, causing white cotton fibers to get all over the crime scene, the CSIs spot a copycat due to the lack of said cotton fibers.
- Daredevil (2015): In the season 1 finale, Matt, Karen and Foggy determine where Leland Owlsley has hidden a corrupt detective who could expose Wilson Fisk, by poring through records dug up by Foggy's ex-girlfriend Marci and noting a specific property that Owlsley has delisted.
- In one episode of Death in Paradise, automated door records, witness testimony, video footage, and the coroner's report all indicate that an out of shape scientist climbed alone up the side of a volcano at night to monitor some anomalous seismic readings, had a heart attack and died. Detective Humphrey looks at the scene for a minute and asks why he didn't have a flashlight...
- Doctor Who:
- "The Sontaran Stratagem": UNIT and the Doctor are investigating ATMOS, a factory they believe is a front for alien activity. While Martha examines the workers and the Doctor sonics an ATMOS device, Donna finds something suspicious: an empty binder for sick days. As Martha manages to determine while doing medical checkups on the ATMOS factory workers, this is because all of them have been hypnotized by the Sontarans (as evidenced by one who says in a never-changing pitch that he works 24 hours a day, and has an abnormally high pulse rate).
- "Nightmare in Silver": Mr. Clever points out that the Doctor erasing all evidence of himself from the universe created this as a side effect: there is now a huge "hole" where he was that is obvious to anyone that's looking.
- "Hell Bent": When Clara gets erased from the Doctor's memories, he is able to reconstruct most of what happened by the shape of the absence left behind.
- Played for laughs in Friends. Joey gives Chandler his show reel in order to be considered for an advert being produced by Chandler's company. When Chandler claims to have watched it, Joey says that he obviously hasn't, because part of the audition tape was a Japandering advert Joey did for "Ichiban Lipstick for Men", which Chandler would have definitely made fun of.
- Law & Order had a case where they realized the killer was following the instructions in a book about how to kill someone and get away with it ("for educational and entertainment purposes only," of course). When they caught the killer and confronted him with all the things he did to (successfully) avoid leaving any clues as to his identity, he responded, "So I'm guilty because you don't have any evidence?"
- Monk's very first case was an example of this; a hooker had OD'd on Promazine — a tranquilizer for horses, pills the size of an adult's eyeballs. Monk's partner at the time, Stottlemeyer, said suicide. Every cop on the scene said suicide. Medical examiner said suicide. Monk walks in, says murder. "Where's the water?" The room had no water! Simple. Eight people in the room, but nobody saw that.
- "Mr. Monk Goes to a Fashion Show": Monk proves that a fashion model's apparent suicide by sleeping pills was staged because the victim was wearing lipstick and there are no lipstick traces on the glass she supposedly drank from, meaning that the killer wiped the glass down then put it back in her hand.
- In "Mr. Monk Goes to a Rock Concert", the clue that suggests to Monk and Natalie that a roadie did not die of an overdose in a port-a-potty is a lack of mud on his boots that would have been present if he'd walked through the muddy patch around the bathrooms.
- In two episodes, "Mr. Monk and the Astronaut" and "Happy Birthday, Mr. Monk", Stottlemeyer concludes that someone else has been to a victim's place of residence from the fact that a computer is missing.
- In the serial killer case documented in the Show Within a Show in "Mr. Monk's 100th Case", this is shown when Monk is at one crime scene, and later turns out to be a clue that allows them to tie the victim to a serial killer:
Adrian Monk: Her lipstick?
Captain Leland Stottlemeyer: Yeah, what about it?
Adrian Monk: It's on the cup. There's some on her lips. But it's not here; it's not in her purse. What happened to the lipstick?
Natalie Teeger: He took her lipstick?
- In Tie-In Novel Mr. Monk and the Dirty Cop, a senile old man supposedly walked across his wet lawn, stood on a chair, scaled a fence, and jumped into his pool to kill himself. Monk proves that it was murder because the man's socks would have been stained crossing the grass, and the socks were bleached white when the body was found. Also, the chair would have sunk into the ground under the weight of the victim, but it was simply standing on top of the grass.
- In The People v. O.J. Simpson, Robert Kardashian's belief in his friend O.J.'s innocence is eventually broken not by the evidence for his guilt, but the fact that even with all the publicity of the trial, no plausible alternate suspect or theory is ever offered.
- Psych: Gentleman Thief Pierre Despereaux was never caught and couldn't have been convicted even if he had been because he never left any evidence behind. It turns out the reason he was able to do this was because he never actually stole anything; he just made deals with museum owners so they could collect the insurance money.
- Raines uses this in the episode "Reconstructing Alice", with a dog that didn't bark, as in the Sherlock Holmes story. Raines even quotes Sherlock Holmes when realizing this.
- Remington Steele: In one episode, a group of mystery buffs enter a game where they dress up as their favorite fictional detectives and run around Los Angeles trying to solve a make-believe mystery. After a while, it turns out the mystery is real, the bodies are piling up, and the game headquarters where the players call in to "report their progress" is nothing but an empty office with an answering machine. After listening to all the leads and clues that were recorded on the answering machine by the players, Laura realizes that one of the players never left a message, and deduces that they must be the one collecting the messages.
- In the Star Trek: Deep Space Nine episode "The Nagus", one of the things that tips Odo off that Zek is not dead is the absence of his bodyguard Mairhar'du (from a species known for their absolute devotion to their masters) at his funeral.
- Vera: In "Tuesday's Child", Vera realizes that a story that the Victim of the Week had left of his own accord is false when she searches the victim's holdall and discovers that he hadn't packed his insulin. As she puts it, why would he leave behind the one thing he depended on for survival?
- Ace Attorney:
- Apollo Justice: Ace Attorney:
- In the flashback trial, Klavier says that, because there weren't any fingerprints found on the gun, the defendant had to be the killer, because he's known for wearing gloves. Anyone with common sense, however, would know that this is faulty logic, because it could be anyone with gloves (and, in fact, Valant also wore them in the night of the crime).
- The victim's insulin syringe in the flashback case is completely empty, adding weight to Phoenix's claim that the killer cleaned it and put something else in it.
- In the extra case from the Nintendo DS remake of the first game, Phoenix Wright: Ace Attorney (MAJOR spoiler): Damon Gant has just "proven" Ema Skye pushed Neil Marshall to his death using a fingerprint-laden piece of cloth he personally cut from Marshall's vest. However, Phoenix notes that while Marshall died of a pierced lung and was coughing up blood on himself for a while before death, the piece of cloth has NO blood on it. Since this proves that Gant cut the cloth BEFORE Marshall died, Gant becomes a bit unnerved.
- Ace Attorney Investigations: Miles Edgeworth:
- In the first case, the killer claimed to have lost his keys and asked a security guard to open the door to "his" office for him. The absence of the security guard's prints on his door suggests that he tricked her into opening a different door that she thought was his.
- In case 5, the absence of blood on the hilt of a knife that was found inside a victim suggests that the hilt was switched, as there were several knives with hilts and blades that fit each other.
- In the third game's second case, the emergency buzzer at the crime scene, which was pressed at the time of the murder, had no traces of prints on it. This is used by Phoenix to prove the victim didn't press it, but the real killer did, resulting in the trope name almost being mentioned.
In connection to the above, later on, the absence of prints is used by Luke Atmey to show that it was Ron who pressed the buzzer, seeing as how Ron was in his Mask☆DeMasque outfit, which meant he was wearing gloves. This statement by Luke would come back to royally bite him in the butt, as there's no way Luke should have known Ron was wearing the outfit; that bit of evidence had only been revealed in the earlier part of that day's trial (and not mentioned since), and Luke had been in a completely different courtroom at the time.
- Comes up occasionally when using the Mood Matrix in Dual Destinies, most prominently when Athena and Blackquill team up to trick Fulbright into an "emotional" confession that was anything but.
- Spirit of Justice:
- Played with in "The Magical Turnabout". Trucy's fingerprints were found in an X-shaped tape understage note , so the prosecution claims she touched it during the murder to have the victim in the stage, not backstage... but she was wearing gloves at the time, meaning she left the prints sometime before the murder. In a nutshell — something that shouldn't be there, was, which proves nothing in this case.
- Double subverted in "Turnabout Time Traveler". At one point, you have to prove that Sorin didn't enter the hold in the night of the crime, and you do that by presenting the hold keycard entry. Because his name is not in the list, he didn't go in. Then Sorin says that he came in using Nichody's keycard. And then, Nichody himself claims that Sorin didn't go to the hold after all, which is the truth.
- Apollo Justice: Ace Attorney:
- In Higurashi: When They Cry, Rena noticed that the bottle of soy sauce in Rika and Satoko's house was missing, and deduced the possibility that they had visited the Sonozaki estate that night with the empty bottle and been kidnapped.
- In Nine Hours, Nine Persons, Nine Doors, the Ninth Man's missing bracelet. It leads Junpei to believe that it was used in Snake's murder, and that killer could open the door with Snake alone, as the bracelet would replace the third person.
- In Virtue's Last Reward, Sigma and Phi use a variation of this involving Dio's behaviour, or lack thereof, to show that the likelihood that he killed Luna is pretty low. With it being in Dio's nature to make a point to draw blame away from himself, the fact that he didn't ask where Luna would be unusual if he killed her. On the other hand, when they where going to go through the chromatic doors, only for Sigma and Phi to refuse, Dio got agitated, saying they were gonna get them all killed. In that situation, if he didn't know anything about Luna's killing, the natural thing for him to have said was Luna isn't present and so they can't go through even if they wanted to [since Luna was in Sigma and Phi's trio for that round]. These two lack of behaviours lead Sigma and Phi to conclude that Dio was a witness but didn't do the killing.
- This is how the first murderer is exposed in Super Danganronpa 2. After the blackout, which was when Byakuya was murdered, Mikan fell over and landed in a... compromising position. Teruteru, of all people, failed to comment on this... which proved he wasn't in the dining hall as he had pretended but under it, from where he stabbed Byakuya.
- This becomes a contradiction in the fan case The Empty Turnabout during Marston's testimony when he claims that he and Ian Arts struggled over Marston's handgun, because the gun only has Marston's fingerprints.
- In RWBY, people with silver eyes are powerful warriors with supernatural abilities. This is a very rare trait, however. Maria Calavera realizes that if silver-eyed people are so powerful, they would have dominated the planet and thus become more common. She uses the lack of this to deduce that someone is targeting and eliminating silver-eyed individuals, so she dons a mask to keep hers hidden. She's later proven right.
- In Grrl Power, this is lampshaded with Sydney's orbs occasionally, as they cannot be scanned by most if any means. Dabbler's scanning spells can't even detect the light they give off. At one point an alien killer robot apparently makes her a priority target because it just sees a black void where an orb would be.
- To Prevent World Peace: How Rhea and Chronos know about the other's presence since their powers can't be used to see anything related to the past/future of the other.
- It's mentioned in Vexxarr that being completely hidden is all but useless, because if people can't find you, they're going to keep looking. Rather, the solution to his endless conundrum of how to hide away from the universe is to either make yourself not worth looking for, or to make it so that people don't want to find you.
- In the Justice League episode Hereafter, Superman is apparently killed by Toyman's latest machine, but Bruce refuses to believe it, and presents his theory to Alfred by saying the lack of evidence is what tipped him off—Toyman's weapon left no trace evidence. It left no debris, so it didn't blow him up. It left no scorch marks, so it didn't incinerate him. It didn't even leave radiation, hence it didn't disintegrate him. Bats decides that since Toyman is merely an obnoxious Mad Scientist, not a god, the Law of Conservation is still in effect, and therefore Superman couldn't have just been destroyed. His conclusion; it teleported him somewhere. He's right - Supes was shunted forward in time, but the show doesn't make it clear whether or not Batman is simply in denial.
- One U.S. Acres cartoon (from Garfield And Friends) has Roy steal the cow Orson was supposed to milk, but was too busy reading mystery novels. Orson and Bo launch an investigation. Their only lead is three sets of footprints. Closer to the end, Orson points out the three sets of footprints which to him indicate three suspects. Bo points out that if Orson's theory is correct, someone's footprints are missing: the cow's.
- The Deputy Dawg Show: "Diamonds In The Rough" has Deputy Dawg tasked with bringing in a diamond smuggler and his contraband. A golfer seems to be way off course as his ball ricochets in DD's office ("I slice badly"). Thanks to Vincent Van Gopher, Deputy Dawg reasons that the golfer is the smuggler and the diamonds are in the ball. When the golfer is subdued and brought in, the sheriff rails at DD because he said they had to have evidence. Deputy Dawg does: he swallowed the ball from an errant shot and it showed in an x-ray at the doctor's office.
- The Bielefeld Conspiracy meme parodies Conspiracy Theories which run on this. Basically, it posits three questions to the person: Do they know anyone from Bielefeld, have they ever been to Bielefeld, and do they know anyone who has been to Bielefeld. Since most people are expected to answer nonote it is concluded that Bielefeld doesn't exist. People who answer "Yes" to the questions are said to be working for the conspiracy, or to have been deceived by it.
- A standard intelligence technique when contacting an agent suspected to be compromised is making an innocuous statement or question and expecting a specific response, also innocuous. If the agent is under duress or has been replaced, the absence of the right response is an indication something may be wrong.
- The redaction of confidential words and phrases from documents can potentially backfire, if the non-obscured context of the redaction makes it clear what sort of information it must contain. It may even foster speculation that's more damning than whatever the actual redacted statement might have been.
- Political scandals often work this way: Some document or thing is questioned. If the person does not address its contents, speculation runs rampant, because after all, if it were innocuous, the easiest thing would be to release it to the press and get it over with. May lead to an underwhelmed reaction when the real thing finally gets out and does not live up to the speculation.
- Warrant canaries.