It can lead to a heartfelt reunion, if the character is desperate for someone to recognize them, but it also might lead to a turn for the worse, if the character can't afford to blow their cover. The pet might also recognize its master's friends, though it doesn't happen as often.
Alternately, it can happen that the pet doesn't recognize its supposed master, who is really a stranger in disguise.
As the trope often deals with The Reveal, expect unmarked spoilers.
- Pokémon: In the Season 1 Kanto region:
- In "Pokemon Scent-sation!", Ash, after being banned from the Celadon Gym, is forced to disguise himself as a girl to get in. Ash's disguise is able to fool even his traveling companions, but Pikachu recognises him all too quickly.
- Prompted by Team Rocket in "Pokemon S 1 E 54 The Case Of The K 9 Caper". They flood the training school with helium gas so all the humans inside have Helium Speech then use a voice changing device to sound like the Pokemon trainers so their Pokemon will follow Team Rocket's orders. It starts working until they try it on Pikachu, who's able to recognize the voice does not belong to the real Ash and refuses to join them. This inspires Officer Jenny to provoke her Growlithe to attack her in order to get close to them and get them to remember the bond they grew with her over training. It works, which leads the Growlithe to go after Team Rocket.
- In Ranma ½, Ryoga's dog Checkers is able to recognize Ryoga even when he's been turned into a pig, despite never having seen his pig form before.
- Batman: In "The Sign of the Joker" (Detective Comics #476, later adapted into the Western Animation example below), Batman attempts to protect one of the Joker's targets by disguising himself and the target as each other. The ploy fails when the target's cat, infected with Joker venom, recognizes and fatally attacks its human.
- Mutts has Earl the dog and Mooch the cat encounter a bizarre, raggedly humanoid with green skin. Mooch panics and advises fleeing the monster. Earl, however, wags his tail, stating: "Green, orange, blue ... I know my Ozzie." Ozzie was mimicking the Frankenstein monster for Hallowe'en at the time.
- In Die 1000 Augen des Dr. Mabuse, the finally un-made-up Mabuse is identified when the guide dog he had been using to play the allegedly blind mystic Cornelius recognises him and runs up to him.
- Diamonds Are Forever: When James Bond is confronted with two apparently identical Blofelds (the real one and a surgically modified actor) he attempts to identify the correct Blofeld by kicking Blofeld's cat, who promptly leaps into one of the men's arms, thus telling Bond who to shoot. Then a second cat enters the room and jumps into the real Blofeld's arms.
- In The Tale of Lost Time, Petya gets turned from a schoolboy into an old man in one moment, and nobody recognizes him except for his dog.
- In Monkeybone, the protagonist Stu resurrected as the corpse of an athlete organ donor and return to his home. His dog comes to him while wagging his tail as if he recognizes his master.
- Inverted in The Parent Trap (1998), where Hallie's dog Sammy barks at Annie when she's disguised as Hallie, much to the maid Chessy's confusion. Later when the two families are at the same hotel, Sammy manages to sniff out Hallie's trail and when he finds her, breaks away from Annie and Chessy and runs right to Hallie (and still managing to not get their cover blown).
- In The Third Man, black marketeer Harry Lime had been declared dead at the beginning of the film, and while looking around Harry's apartment Holly learns that Harry's cat would only get close to Harry. At a crucial moment in the film, Harry's cat is shown approaching a figure in the shadows, until a light is shined on a not-so-dead Harry.
- Inverted in Kagemusha; a thief who bears an uncanny resemblance to a Samurai warlord serves as the warlord's double. When the warlord dies, the double is able to convince the warlord's retinue and even his children and grandchildren, but the warlord's horse recognizes that it's an impostor riding it, and the horse throws its rider. When the impostor's thrown, people see that he is missing the warlord's battle scars, revealing the nature of the deception.
- In Anne's House of Dreams, Dick Moore's dog Carlo doesn't recognize its master when the latter returns, mentally disabled, after a long voyage. The man's sanity is restored thanks to a new successful treatment, and it turns out he is in fact Dick's almost identical-looking cousin.
- In Elephants Can Remember by Agatha Christie, the family dog bites its longtime mistress Margaret. It is one of the clues that Margaret has really been replaced by her twin sister Dorothea.
- In one of the tales in The Old Nurse's Stocking Basket by Eleanor Farjeo, a Prince and Pauper switcheroo is only resolved thanks to the two boys' dogs recognizing their masters with no hesitation.
- Older Than Feudalism. In The Odyssey Odysseus's dog Argos is initially the only one to recognize him when he returns from his adventures.
- Sherlock Holmes has solved more than one case by observing the behaviour of pets around their owners and/or the owner's imposter:
- In Holmes' adventure of Silver Blaze, the curious incident of the dog in the nighttime is that it doesn't bark, thus showing that it was familiar with the man who stole the titular horse from the stables: namely, John Straker.
- Holmes uses a dog to help solve The Adventure of Shoscombe Old Place. When released, the dog bounds towards his mistress' carriage, but snaps angrily at her when he gets close. Holmes realizes that the "woman" is an imposter — actually her brother in disguise. The man had given the dog away in order to avoid such a reveal.
- The Dukes of Hazzard - inverted in the episode "The Dukes Of Hazzard S 6 E 3 Too Many Roscos". The criminal mastermind Woody who is impersonating the titular Sheriff Rosco has an encounter with Rosco's dog. The dog is quick to growl at the imposter and Woody has to come up with an explanation.
- A well-known case in Judge Judy is when a woman stole a man's dog and kept him as her pet while claiming that the dog has always been hers. As soon as the dog was brought into the court, Judge Judy ordered the woman's sister to put the dog down, and the dog instantly ran to the man full of happiness. Judge Judy said "that's his dog" and dismissed the case.
- In the Perry Mason TV series episode "The Case of the Bashful Burro," Perry calls Amos Catledge's burro as a witness during trial. As soon as the burro enters the courtroom, the animal affectionately nuzzles his master (who has shaved and gotten a haircut to change his appearance, and is watching the proceedings after going into hiding), thereby exposing him and forcing him to testify.
- On Revenge, Amanda Clarke's old dog Sammy remembers her when she returns to the Hamptons as Emily Thorne, but doesn't like the woman Amanda/Emily switched identities with.
- In the sequel to Ace Attorney Investigations: Miles Edgeworth, the murder investigation at the prison uncovers a breakout attempt by one of the prisoners. Said prisoner was wearing a guard uniform as a disguise, but he gets outed when his pet polar bear walks up to him.
- Batman: The Animated Series: Used tragically in the episode "The Laughing Fish" when Batman, in order to protect a man from the Joker's murderous plot, switches place with him. Unfortunately the Joker chooses to use the man's infected pet cat as his weapon.
Batman: Even drugged, the cat knew to go for its owner.
- The Flintstones: In "Rip Van Flintstone", Fred dreams that he's been asleep for 20 years and goes to see Barney, who is now a multimillionaire. However, Barney had met several phonies claiming to be his missing friend, so he proves Fred's identity by calling in Dino, who promptly pounces and licks his old master like always.
- The Mask: Zig-zagged in "The Aceman Cometh", where Ace Ventura is able to deduce that the Mask is Stanley Ipkiss due to Milo's fondness for him - and also because his pet monkey Spike took pictures of Stanley transforming.
- In the Mickey Mouse version of The Prince and the Pauper, Pluto runs up to the Prince pretending to be Mickey, but after licking him and sniffing him he instantly realizes he's not his loyal master and leaves him. Later, after the climax, both Mickey and the Prince are together and no one can tell the other apart. No one, that is, except for Pluto, who charges Mickey and smothers him with kisses.
- Steven Universe: In "Escapism", Steven possesses a Watermelon Steven, building a boat and sailing it to Beach City in an attempt to get help; the boat gets capsized and Steven floats aimlessly in the water until Lion happens upon him. The big cat quickly realizes it's Steven in there and carries him to the Temple.