So you have a scene set up, the villain is ready to commit some horrific crime, how do you make the scene even scarier? How do you establish this is a particularly depraved and dangerous individual, without any tension breaking exposition or over the top acting? Quite simply, have them whistle.
Amongst humans whistling is an almost universally understood expression of joy. As such portraying the villain cheerfully whistling away, quite often to a well-known upbeat tune, a piece of classic music or a nursery rhyme, is a wonderful quick way of establishing someone truly depraved enough to enjoy their vicious acts, the cheer and calm created by the whistling contrasting sharply with the horror created by their depraved acts.
There are generally two versions of this: in the first the villain will be portrayed as whistling because they are genuinely happy, displaying their sadism and cruelty. In the second, the tune will be slow and stilled and the villain instead comes across as detached and almost bored. The whistling is their way to make the time go faster, thus emphasizing their sociopathy and their non-reaction to such horrific acts.
Like all variations of Subverted Innocence, the idea of turning something so benign and sweet so much on its head, the sheer feeling of dissonance this creates is guaranteed to make any scene featuring it much scarier.
If used enough that it can become the villains Calling Card, then expect there to be at least one scene where we don't see the villain, we can just hear them whistle, as they stalk the latest target, leaving the audience constantly on edge that someone is about to die.
Compare Ironic Nursery Tune, Tuneless Song of Madness and Ominous Music Box Tune, which employ similar subversions of innocent tunes and rhymes for Nightmare Fuel. Also Wolf Whistle which is used specifically to sexually harass people. Contrast Not-So-Innocent Whistle when whistling is still used to hide a misdeed, but is played for comedic effect rather than horror.
- Fullmetal Alchemist: Envy happily whistles when Mustang agrees that humans are easily manipulated. Additionally, in the manga, Envy often has musical notes added into their dialogue, though they are removed in the English version.
- Kite in Yu-Gi-Oh! ZEXAL does this occasionally as an intimidation tactic. Notably, in the Japanese version, it's a theme associated with his younger brother Hart, while it's only a generic tune in other versions.
- Mechamato: Janitoor is fond of whistling ominously while on the prowl. The lights in Pian's house go off shortly after he hears his whistling, then Amato, Deep and Pian hear it again before Janitoor laughs evilly and attacks them.
- Big Finish Doctor Who: In the episode Night Thoughts, the killer stalking the island can be heard whistling "Oranges and Lemons" while hunting down the university researchers. It's because the killer is actually a girl the researchers killed over the course of their space-time experiments, now brought back from the dead by their newest success; according to her mother's suicide note, "Oranges And Lemons" was the girl's favourite nursery rhyme.
- Constantine (2005): After finally securing the rights to John Constantine's soul, Lucifer begins cheerily whistling as he drags him off to hell. Thankfully, God stops him at the last minute.
- G.I. Joe: The Rise of Cobra: Terrorist organization Cobra operative Zartan whistles "For He's A Jolly Good Fellow," several times throughout the movie, including when he murdered Cover Girl and the ending where he replaces the President of the United States and takes over the White House.
- Hanna: Isaacs, the sinister assassin hired by Wiegler to track down Hanna, enjoys whistling to himself while hunting his prey. Also doubles as In-Universe Soundtrack, as the song, The Chemical Brothers' "The Devil is in the Details", is heard playing at Isaacs' nightclub during his introduction.
- Jeepers Creepers: The titular Creeper is shown to have a fondness for the song its named after, casually whistling it from time to time, including when its stalking its victims or making its "art" out of its victims remains.
- Jonah Hex: In one scene Burke is shown happily whistling a tune to himself whilst he sets up the explosives to blow up the train.
- Kill Bill: Elle Driver infiltrates the hospital in a nurse's outfit, intending on giving a lethal injection to the comatose Bride. She happily whistles away to herself during the entire thing, the tune in question being the "Twisted Nerve" theme.
- M: In what is probably the Trope Maker, the titular child killer whistles "In The Hall of The Mountain King" right before he tracks down his victims. This is used to great effect, with many scenes keeping the killer off-screen; meaning the whistle itself carries the dread. The tune itself contains multiple pauses and breaks in odd places, giving it an additional sense of wrongness. As Peter Lorre could not whistle, it was the director Fritz Lang himself who provided the iconic tune.
- The Stepfather: The titular Stepfather often whistles the tune of "Camptown Races" to himself, usually after he commits a murder.
- The Shawshank Redemption: Just after the warden has Tommy murdered, the scene cuts to his office where he comes in and tells Andy (freshly back from his torture in solitary confinement) to hurry up with the accounting. After stashing the records of his corrupt dealings in his safe, he walks off, nonchalantly whistling a Christian hymn ("A Mighty Fortress is our God").
- These Are the Damned. King's gang of Teddy Boys whistle the tune to "Black Leather Rock" while marching off to mug Simon, and later for signaling while they're hunting Simon and Joan in the graveyard.
- In the 2010 film The Traveler, the malevolent ghost Mr. Nobody whistles the first lyrical sounds of Mozart's Lacrimosa as he goes about killing the police officers who had him murdered. Best seen here.
- The British thriller Twisted Nerve, a Trope Codifier, has the murderous Stalker with a Crush Martin whistling the film's infamous tune as he follows Susan on foot around the city. The theme has become synonymous with the trope, seeing shout-outs in Kill Bill and American Horror Story where the tune was also whistled under similar circumstances.
- Airman: Bonvilain whistles a classical piece at one point, highlighting his Wicked Cultured status.
- The Pilo Family Circus: Jamie's secondary personality (AKA JJ) finally proves himself every bit as vicious as the other circus clowns when he takes an axe and goes on the prowl for victims while whistling "Que Sera, Sera".
- In P D James' Devices and Desires, women in Norfolk are being killed by a serial killer known as the Whistler, because he'd been heard whistling a hymn after one of his murders.
- American Gothic (1995): In one episode, Affably Evil Buck comes into a jail with obvious evil intent— and is whistling the theme to The Andy Griffith Show. It's creepy as all get out.
- American Horror Story: Murder House: After snapping in 1996, Tate Langton whistles the "Twisted Nerve" theme whilst perpetuating a school shooting.
- The second Count Vertigo, Werner Zytle, is fond of whistling "In the Hall of the Mountain King", while going about his work.
- In "Disbanded", after murdering the guards tasked with protecting him, Adrian Chase/Prometheus drives back while listening and whistling to the tune of "It's a Beautiful Morning" on the radio.
- Bonanza: In the episode "Justice Deferred", a man named Frank Scott is hanged for strangling a woman to death. But it turns out the real killer is Mel Barnes, who is the spitting image of Scott, and has a habit of whistling "On Top of Old Smokey". Used as a plot point as it identifies him as the true culprit.
- Breaking Bad: Jesse is distraught over a TV news broadcast about the disappearance of Drew Sharp, the boy that Todd killed. Walt tells him that he feels guilt about the incident as well, but after the conversation is over, he starts to whistle light-heartedly, implying that he doesn't feel any remorse at all.
- Chernobyl shows a heartbreaking variation in episode 4 when Pavel, joins the squad of Bacho and Garo, as part of the "Animal Control" unit. Their mission is to hunt down abandoned pets and livestock, and put them down so they don't spread radiation outside the containment area. On their first patrol, Bacho shows Pavel the tried and true technique to attract their quarry, which is to whistle the way a dog's owner would to attract their pet. This causes a pack of dogs to happily come out of hiding and enjoy some human contact, which allows the squad to gun them down as quickly as possible.
- Cold Case: "Sabotage" features Alessandro Rossilini a terrorist bomber who whistles "John Henry", due to a childhood fascination with the story, while setting up his bombs.
- In "Coda" Peter Matthews (the younger of the Matthews brothers) whistles tunelessly to himself as he advances on Joan Thursday and the other hostages they've taken.
- Whistling "Antonio" in a slow and stilted manner is the Calling Card of the Towpath Killer from season seven. This is used to great effect, with several scenes involving the killer entirely offscreen and we just hear him whistling as he closes in on his victims. It's likewise used as a plot point twice first to identify his copycat isn't the real killer as he instead whistles Molly Malone and second to cause Sergeant Strange to realise Carl Sturgis is the real killer when he starts whistling Antonio in his kitchen.
- Jane the Virgin: Crime lord Sin Rostro is often heralded by a signature nine-note Leitmotif, which they sometimes whistle themselves.
- Jekyll: In keeping with his characterization as a Psychopathic Manchild, Mr. Hyde has a habit of whistling "Boys and Girls, Come Out to Play" — most notably after breaking a young man's neck and expressing a desire to "play lions" with his girlfriend.
- Legends of Tomorrow: Big Bad of Season Four, Neron is shown to have a fondness for "Pop Goes The Weasel", leading to one particularly nightmarish scene where he's casually strolling down the street slowly whistling it to himself whilst all around him his influence causes fights to break out, murders to occur and cars to crash. Used as a plot point as after he is seemingly killed it's revealed he possessed Ray Palmer, when Ray starts whistling the same tune.
- Midsomer Murders: "Echoes of the Dead" features a killer who murders people they believe committed a crime against the sanctity of marriage. At the end of episode, as he stalks his latest victim trying to bludgeon her to death with a sledgehammer, he happily whistles "Here Comes The Bride" to himself.
- Police Squad!: A thug disguises himself as "press" to bring a large number of weapons into a victim's room and kill him. The guard doesn't notice. Whistling "Whistle While You Work" on the way out probably helped.
- Power Rangers RPM: In "Go For The Green", one of the protagonists, Ziggy, encounters Tenaya 7, an android created by the evil A.I. Venjix to infiltrate Corinth, for the first time after she tries to go incognito as a civilian in the hope of passing his audition for the Green Ranger morpher. After Tenaya's cover is blown, Ziggy flees from her with the morpher and finds himself cornered in an area where sheets are drying. As he calls Dr. K for help, he hears Tenaya stalking him while whistling "The Farmer in the Dell", appropriately enough. This is actually a plot point as, up till this point, none of Venjix's robots have expressed much emotion beyond Crush, Kill, Destroy!
Dr. K: I'm on my way. I'll track you through the morpher.
Ziggy: Yeah, well hurry, 'cause - this one's different.
Dr. K: Different? Different how? Explain.
Ziggy: Well, she's...[hearing Tenaya whistle and visibly disturbed]...she's enjoying this.
- The Walking Dead: The Saviours (led by Negan) are recognizable by their two-note whistle.
- The Wire: Downplayed. While he's a better person than the vast majority of the cast, Omar Little is still a vicious criminal who exploits this trope, whistling "The Farmer and the Dell" as he robs (usually even worse) people.
- Brazilian Folklore: The Saci-Pererê, the Curupira, the Caipora and the Comadre Fulozinha often whistle as a way to scare travellers and hunters away in the middle of the night. The closer the sound seems to be, the more far away they are from the victims, making them get lost in the forest.
- El Silbón ("The Whistler") from Venezuelan folklore is the malevolent spirit of a man who murdered his father and was thus condemned to carry his bones for all eternity. He's described as having a characteristic whistle note and just as with the beings from Brazilian folklore, it is said that when the whistling sounds close, there's no danger, and El Silbón is far away, but when the whistling sounds distant, it means he is nearby.
- On The Saint Radio Drama, the producers were unable to show the Saint's Calling Card of a haloed stick figure, they instead gave character a distinctive, and slightly unsettling, whistled tune. The Saint (played by Vincent Price) would whistle it during the show's intro, and often whistle to unnerve crooks as he was getting close to them.
- Back in the Golden Age of Radio, The Whistler was the narrator/host of an anthology mystery series. Like the first years of The Shadow, the otherwise-nameless tunesmith did not participate directly in the action, but rather provided ironic and somewhat sadistic commentary on the twists of fate that led to the (usually criminal) main character's downfall. The whistling, however, was just as sinister as the Shadow's laugh. (The radio drama would spawn a successful B-Movie series directed by William Castle and a one-season TV drama in The '50s.)
- In Chronicles of Darkness: Innocents, one of the potential threats the young player characters can face is the ghost of a Serial Killer by the name of Red Dan, easily recognized by his habit of whistling a merry tune. These days, Dan enjoys possessing children so he can force them to commit crimes and watch them gradually lose their minds in the process; however, an easy way of identifying the kid that he's possessing is the fact that they begin to compulsively whistle as well.
- Dungeons & Dragons: Whistlers are Humanoid Abominations that appear as lanky gray figures constantly flickering in a state of "perpetual physical uncertainty." They get their name from how they telepathically whistle an eerie, otherworldly melody that only one or two other creatures can hear. This "invades and scourges the mind" of listeners, dealing a nasty amount of psychic damage, and can make victims frightened of the whistler. Those who survive a whistler encounter are forever haunted by its soundless, seven-note tune.
- In The Mousetrap, the unseen killer can be heard whistling Three Blind Mice right before the murder. The killer repeats the whistle after their identity is revealed.
- Metal Gear Solid 4: Guns of the Patriots: The villainous members of La Résistance throughout Prague are happily whistling away, enabling you to track them. It straddles the line between silly and eerie.
- Team Fortress 2: In the conclusion of the "Meet The Pyro" trailer, the Pyro can be heard whistling a Dark Reprise of "Do You Believe In Magic" by the Lovin' Spoonful as he departs the battlefield, leaving the bodies of the entire BLU team in his wake.
- The Witcher 3: Wild Hunt: Gunter O'Dimm, the mysterious, magical, and sneakily malevolent merchant in the DLC Heart of Stone has ominous sounding theme music. You first hear Creepy Children Singing it as Geralt enters the town. Later Gunter himself whistle sit as he walks away tossing and catching a skull in his hand if he is able to collect Olgierd Van Everec's soul.
- In the first Dark Fall game, The Journal, your character's brother mentions hearing a ghost whistling outside the abandoned Dowerton train station. You can also hear this ghost from a certain vantage point in the nearby Station Hotel.
- LISA: The Painful's antagonist Buzzo has a Leitmotif, Joy Boy, that is entirely comprised of whistling. Whenever it's heard, something bad is almost guaranteed to follow.
- The Last of Us Part II: The Seraphites, while capable of verbal communication, largely use eerie whistling to communicate while out in the field. This can range from hushed whistles to alert other Seraphites to a disturbance to loud, shrill whistles to put all Seraphites in the area on high alert. This, combined with their odd lingo, makes Seraphite communication difficult to understand to any enemies.
- No More Heroes Desperate Struggle: Margaret Moonlight introduces herself with an eerie whistle that, according to Sylvia when she is narrating the events of the story, knocked her out for a week.
- Amphibia: General Yunan engages in this when coming to meet Grime and Sasha.
- One voiced Pink Panther cartoon series had an episode about catching a burglar only known for his habit of whistling "Pop Goes The Weasel".
- Total Drama: The Big Bad of All-Stars, Mal, loves to whistle "In the Hall of the Mountain King" often after he's just done something awful to one of the other characters. It even becomes a case of Something Only They Would Say as it allows Duncan to remember him from when they were in juvie together.
- Trollhunters: Nomura whistles "Hall of the Mountain King" to unnerve Jim. It turns out she saw the opera and really enjoys the tune.