They Have the Scent

Dogs have been brought out to track some quarry and have been sniffing about. One starts to bay, and the others join it, and they all chase off.

Because They Have the Scent. And someone will say so. In these words, or others. It's sometimes "They've picked up the scent." or "They've picked up the trail." The second may also be used when the Scarily Competent Tracker is clearly following.

If the dogs are hunting people, they are loud enough to be heard by the pursued, who may be the ones who say this. It indicates that The Chase is about to begin in earnest, and that evasion will not be feasible, or require throwing the dogs off. Generally a grim point. And the pursuee will almost always go to water or roll in something disgusting to throw the animals off the scent. (This always works on television. Contrary to what most people expect, it does not work in real life.)

Hunters of either animals or men may also use the Stock Phrase.

This is also used in superhero comics wherein you have a hero with animal powers, or with aliens/fantasy races with strong senses of smell. May be visually represented with Fluorescent Footprints or a glowing "cloud" of scent.

Comic Books

 * Tintin's dog Snowy regularly picks up trails. He's not usually successful, though; on at least one occasion he was actually going after a bone rather than the criminals Tintin was trying to catch. Tintin also scatters pepper in one story to put an enemy dog off the scent.

Fan Works

 * In With Strings Attached, George becomes a dog in order to track Ringo, who has run off into the forest to escape the craziness in Aurion's tent.

Film
"Aragorn: [about the orcs] Their pace has quickened. They must have caught our scent. Hurry!"
 * Lord of the Rings: The Two Towers

"Sid: My family abandoned me. They kinda migrated without me. You should have seen what they did last year. I mean, they got up early, and quickly tied up my hands and feet, and gagged me with a field mouse, and barricaded the cave door, and covered their tracks, and went through water so I'd lose their scent, and... and... who needs them anyway?"
 * Inverted in that it is the orcs that are being pursued, and they've caught the scent of their pursuers (Aragorn, Legolas and Gimli) and are speeding up so they won't be caught.
 * Ice Age: Invoked


 * Willow has the hell dogs, which Bavmorda sends to track down the escaping nursemaid in the opening sequence. The nursemaid barely makes it to the water in time to drop the baby on a raft before the hell dogs are upon her.
 * Maximus tracks Flynn this way in Tangled. (Maximus, by the way, is a horse.)
 * In Lady and the Tramp, Trusty is a retired tracking bloodhound who has lost his sense of smell. When the Tramp is taken to the pound, Trusty tries to pick up the scent. Joq at first feels sorry for his old friend and tries to make him admit he can no longer track, but Trusty scoffs it off and continues. Against all odds, he manages to pick up the scent and arrives just in the nick of time.
 * In Shrek Forever After, Shrek gives Fiona's handkerchief to Donkey so that he could pick up the scent and find her. Donkey is at first insulted about being treated like a dog, but then smells something and goes after it. It turns out to be waffles set up as bait for a trap, although it does lead them to Fiona.
 * In The Fox and the Hound (film), Cooper first meets Tod by tracking his scent.

Literature

 * In Dan Abnett's Gaunt's Ghosts novel Traitor General, Landerson recognizes the sound and tells Gaunt that the dogs the Chaos forces are using have their scent.
 * In Blood Pact, the Chaos forces transform one of their number to do this, and later, when Mkoll picks up Gaunt's trail, Kolea phrases, "He has the scent."
 * In Discworld, once criminals start hearing that a werewolf has joined the watch, they grow wise and carry 'scent bombs': a thin glass vial of peppermint oil or aniseed oil is shattered in a busy intersection, where hundreds or thousands of people will walk over it, obscuring the criminal's scent with theirs. Also, Moist Von Lipwig has an emergency escape plan (hatched after he heard the watch employs a werewolf) including detours through the butchering district and riding dung carts.
 * Except that this won't work, since Angua can track a suspect through those. The one that does get her is the spice market.
 * In the Sherlock Holmes, story The Sign of Four, one of the criminals steps in creosote leaking from a cracked carboy. Holmes sends Watson to borrow "Toby", a homely mongrel with an amazing nose. At one point, Toby is confused when their quarry crosses paths with a creosote-soaked barrel on a hand trolley and follows the false trail, but they take Toby back to the spot where he appeared confused and he once again picks up the correct trail.
 * Toby also makes an appearance in The Seven-Per-Cent Solution.
 * In N or M, Agatha Christie's Tuppence Beresford has rubbed aniseed oil on her shoes so that she can be followed by the officials when she goes to meet a suspected spy. When the person escorting her to the meeting tells her to get into a car,
 * In William King's Warhammer 40,000 Space Wolf novel Grey Hunters, Sven and Ragnar know there is trouble when they see the Chaos forces have dogs sniffing at a trail.
 * In Graham McNeill's Warhammer 40,000 Ultramarines novel Courage and Honour, when two dogs grow frantic, Uriel does not use the phrase, but goes to check himself, and smells human blood.
 * In John C. Wright's The Orphans of Chaos, when Grum sets Lelaps on Vanity and Amelia's trail, he finds them, turns away, and starts to bay, running off. Grum comments that he's found the scent.
 * In Robert E. Howard's "Red Nails", when Conan the Barbarian and Valeria are inching away from the dragon, the wind abruptly blows directly from them to it. Its reaction is instant, and they run.
 * In Poul Anderson's A Midsummer Tempest, they get the dogs on Rupert and Will's trail.
 * Stephen King's The Green Mile plays with this. A group of dogs tracks the two kidnapped girls at the beginning of the story, but they get mixed up at the creek; two of them want to go in another direction. After the scent is reestablished, they go with the rest of the pack. Later, Paul figures out that it's because those two dogs weren't police dogs, and got the smell of the killer and the girls mixed up in their head, so that when the killer ditched the girls at the creek, they went in his direction, rather than where the girls were eventually taken by John Coffey.
 * That is, the tracking dogs had to be primed with a scent, and the scent they were given was of the girls. The police dogs caught the third scent mixed up with them, and knew from training that that was the real target, and tried to hunt that down. The others track what they were given to track. Where the two diverge, they disagree. When they find the scent of the girls minus the third scent, they all chase that down. The search party makes the obvious assumption when the dogs lead them to what is found- a blood-covered Scary Black Man with the mangled corpse of a white girl in each hand. Poor Communication Kills.
 * Matthew Hawkwood and Lassuer are hunted using dogs in Rapscallion.
 * In one of the Tarma and Kethry short stories, two kidnapped girls drop shreds of white silk out of the wagon they're being transported in. The silk is invisible against the snow the wagon is rolling through, but leaves traces of their scent that Tarma's kyree familiar Warrl can follow.
 * In Gene Stratton Porter's Freckles, they try to use bloodhounds to find Black Jack. They follow his trail an amazing amount, but finally lose him in the depths of the swamp, which is attributed to snakes frightening the hounds.
 * In Devon Monk's Allie Beckstrom novel Magic To the Bone, Allie recounts how, to throw a Hound off your trail, you need to avoid using magic and cover up your smell with something else stinky. She opts for garbage.

Live Action TV

 * MythBusters busted pretty much all of the traditional methods of throwing a dog off the scent: just about the only place you might conceivably lose a scent dog is in an urban environment, where there are too many other scents for the dog to concentrate on yours. Unless they're using a dog that has been specially trained to ignore all other city scents, as they demonstrated. In which case you're screwed.
 * The Tenth Kingdom. Tony has asked Prince to sniff for clues. Prince instantly responds that (since they're in a farming village) it's mostly excrement at ground level, and there are hundreds of minor scents. Tony then flatters Prince by saying that a master hunter like himself should be able to find the scent they want instinctively. Prince says, "Correct," and off they go.
 * Leverage: A militia group uses hunting dogs to chase Eliot and Hardison in "The Gone-Fishin' Job".

Music

 * "Ol' Red" is a tune about a prison guard dog with this ability, and how a prisoner evades it.
 * In Limp Bizkit's music video for "Eat You Alive", police dogs are shown sniffing out the scent of the woman the band has kidnapped, and they give chase.

Video Games

 * The Legend of Zelda: Twilight Princess is a game example, where you are the one who picks up The Scent (in wolf form,) with many different smells presented throughout the game.
 * Discworld Noir.
 * The titular hero in Batman: Arkham Asylum. With his (bat?)scanner he can extract separate essenses (like tobacco stains or alcohol vapors) and then pinpoint them in the surroundings to track the smoker/drinker.
 * Not exactly dogs, but in the opening cutscene of Halo 3 the Arbiter warns a group of humans: "We must go. The Brutes have our scent."
 * To which Seargeant Johnson replies: "Then they must love the smell of Badass."

Web Comics

 * Schlock Mercenary makes use of the eponymous amorph ability to track by scent. Of course, this works only so far.
 * In The Specialists, the dogs start to bay once on the trail.
 * In Rusty and Co, why you should not smoke: monsters hunt by smell.
 * In Order of the Stick, at one point they follow Belkar's nose.
 * Girl Genius has "wasp eaters" - many-legged weasel based constructs who start screeching when they smell a Slaver Wasp, Revenant (anyone into whom an enslaver has implanted) or Geisterdamen (probably because they work with hive engines). Being weasels, they also can attack  on their own.