Squids squirt ink to create a substitute to escape their predators. It's an oily substance, difficult to dissolve in water, that becomes a sort of mass. On the other hand, octopi use ink as a smoke screen. It is water soluble in order to spread. Like oil and water, even the inks of the two species doesn't mix.
Sometimes, different species, such as cats and dogs, are written so that they have a built-in and unquestioned animosity for no other reason than that they are stereotypically considered to be adversaries. A dog that doesn't chase cats will be considered 'weird', even if they were raised together from birth. On the other hand, those same dogs will almost never chase after mice unless provoked.
Real Lifeis more diverse: there are dogs who bully cats, and there are cats who bully dogs. There are also plenty of cats and dogs who get along very easily and even like each other. Both will usually eat mice.
See also Cats Are Mean. Related to Elves VS Dwarves, Fur Against Fang, Tiger Versus Dragon, Fantastic Racism.
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Anime and Manga
Pokémon; the mutual hatred between Zangoose and Seviper (see below in Video Games) became a plot point in a Diamond and Pearl episode, when a far too single-minded pack of Zangoose attacked Jessie's Seviper repeatedly throughout the episode, ultimately threatening to push it (along with Jessie herself, the rest of Team Rocket, and half the heroes' Pokémon) off a cliff.
Also, in "Showdown at Dark City", Electabuzz and Scyther are stated to be mortal enemy species.
Tiger vs Dragon and Dog vs Monkey appear to be Japanese versions of the dog/cat thing, since they're alluded to often in anime and manga.
In a one panel gag, Sangatsu no Lion once uses the snake and mongoose rivalry as a visual metaphor for a heated argument between Rei and Nikaidou.
In Ginga Nagareboshi Gin: Dogs and bears are mortal enemies. The whole plot revolves around the dogs gathering enough "soldiers" to battle the bears, and the actual battle itself. Though the protagonist is able to overcome this, as shown when he got upset after seeing another dog kill two innocent bear cubs.
The dogs of Garfield (minus Odie) enjoy this, and he's asked them why on more than one occasion. They never come up with an answer.
Garfield also subverts this trope by befriending a mouse named Floyd (and letting him bring other mice over for house parties), much to Jon's annoyance.
Gear is about a war between four nations of small cats, larger cats, dogs, and insects, doing battle by means of Humongous Mecha!
The basis for the animal metaphor in Art Spiegelman's graphic-novel-style biography about his parents' experiences in the Holocaust, Maus. The Nazis are portrayed as cats, the Jews as mice; other nationalities are also portrayed as animals, depending on certain stereotypes of those nationalities and those animals.
Same deal in the Manga Apocalypse Meow, except it's a Japanese writer examining the Vietnam conflict. Americans are rabbits, Vietnamese are cats, Russians are bears, Chinese are pandas, French are pigs, and Japanese are monkeys (including an unflattering Author Avatar).
The trope is subverted in Captain Carrot and the Final Arc; the real murderer is revealed to be Alley's magically created Evil Twin, and the true Alley vows to resurrect Little Cheese.
Interestingly, the story of Little Cheese' murder by Alley Kat Abra was apparently written under editorial fiat- Scott Shaw! (yes, the exclamation point is part of his name), the creator of the characters, when encountered at a Con, said that he was strongly opposed to the story idea, but told he had to do it anyway. The 'evil twin' retcon was his just revenge upon those editors after they'd gotten the boot.
Considering on Earth-C, cats and mice * don't* hate each other (and any cat or mouse that did would be considered a bigot/speciesist), it makes the above-cited "reason" as all the more out-of-character for Alley (and thus should've given reason for the Crew to be suspicious). Supporting this is one story where the Zoo Crew, while visiting other dimensions briefly, encounter one resembling Tom and Jerry; Alley found the sight of seeing "a planet terrorized by...primitive felines" to be disturbing.
Partially subverted in the comic strip Pearls Before Swine, using sensitive, intelligent character Zebra, whose never-ending efforts to reach detente with various predators (lions, more recently crocs) inevitably fail miserably. In one strip, he writes a moving letter asking why; the lions' response is 'Yu taste gud!'
In Peanuts, Snoopy has always hated cats. On many occasions, he has taunted the "stupid cat next door".
Only for the cat - whose name is eventually revealed as "World War Three" - to promptly scare him in return (usually shown as the unseen cat SWIPE!-ing a huge chunk out of the doghouse). The only time Snoopy ever beat that cat is when he thought Woodstock was in danger.
In one of the many, many (in canon) Supergirl series for DC Comics, it is revealed that the rivalry between cats and dogs is based on ancient cat-gods and dog-gods, a fight that still goes on in another realm today.
French noir-style Funny Animal (well, not really funny, it's mostly dead-serious)) comic Blacksad has a rather dark twist on this in its second tome, Arctic Nation- the eponymous organisation is that world's equivalent to the KKK and paramilitary neo-nazi groups, only made up of white-furred or feathered anthropomorphic animals who hate dark brown- and black-colored animals, even if the same species. There's also a less-seen Black Panthers equivalent for good measure.
Cubitus: Cubitus the dog and Sénéchal the cat are sworn enemies and rivals who take delight in beating each other up.
Tom Poes: No jingoism seems to exist between the animals based on their species. Tom, a white cat, gets along fine with Joost, the dog butler and Bullebas, the dog police chief.
In Nico The Unicorn, mountain lions and unicorns are said to be natural enemies. This proves true when one kills Nico's horse mother.
Reynard The Fox: Reynard is considered to be the rival of Isegrim the wolf.
Averted in the A Cricket In Times Square series by George Selden, which features a mouse (Tucker) and a cat (Harry) who are best friends. A flashback book even averts Cats Are Mean by having Harry be the one to initiate the friendship in the first place. A later book even has the pair adopting an orphan puppy.
The ancient enmity between rats and humans is also subverted. Between rats and terriers, not so.
Explained in an African folk tale. According to the story, Cat and Dog were once great friends and did many friendly things together. But then came hard times and Cat and Dog had to go their separate ways. Dog wandered off and Cat found a human family to shack up with. Dog eventually went to Cat and begged to be allowed in so he could get a decent meal. Cat took pity and directed Dog to his owner's brother, but not before extracting a promise that Dog not come back. Dog kept his promise for a while, but eventually either forgot or judged that circumstances rendered the promise moot, and shambled on back to see Cat. Cat was pissed, to say the least. So dogs aren't chasing cats because they hate cats-they want to be friends again, and cats still refuse to forgive.
You could almost say he's the original Dogged Nice Guy. (Kill me. I can't stop myself.)
Many other animals don't come off looking too good in the mythology of Watership Down. Dogs in particular are portrayed as incrediblystupid compared to the Guile Hero El-ahrairah.
Redwall has many varieties of this (though the animal characters are essentially humans with fur). Rats and mice have disliked each other from book one. Raptors are hostile toward prey species until they've been properly introduced. Four-legged predators (except for badgers and otters) are usually antagonistic throughout the story.
Often appears in books by Dick King-Smith. Sheep and dogs in The Sheep-Pig (filmed as Babe) are both convinced the other is irredeemably stupid, and sheep also refer to dogs as 'wolves', refusing to believe they have truly changed their nature. Martin's Mice is about a cat who hates the idea of killing and eating mice and eventually tries to keep them as pets. The more conventional cats vs. dogs one shows up in Ace, with the Deadpan Snarker cat a more sympathetic character than the snobbish dog (who believes that being a corgi grants her some kind of royal status).
In Rudyard Kipling's The Cat That Walks By Itself, after the cat can't resist giving a snarky answer, the dog declares that it will chase cats, and the story ends with the statement that this is why dogs to this day usually chase cats.
Played with in The Incredible Journey with Bodger the bull terrier and Tao the Siamese. The two of them both hate (other) cats, and because of this are best friends, having bonded by terrorizing the local cat population together.
Played dead straight in Tailchaser's Song, in which the cats even have a legend that serves as an Origin Story for the rivalry between their kind and dogs.
Live Action TV
Several Wesen species in Grimm are enemies; the wolf-like Blutbaden vs the pig-like Bauerschweins, the snake-like Lausenschlange vs the mouse-like Mauzhertz, etc.
In Dungeons & Dragons 3.5, this was completely averted with the guardinals. Thanks to the nature of these celestials as warriors devoted to the highest good (and only good), none of the various species ever (or rarelyever) come into conflict, not even such "traditional" enemies as cats and dogs. One of the clearest representations of this is described in the Book of Exalted Deeds with Talisid and the Five Companions: not only does Talisid consider all of the companions his closest friends, acting more like an epic adventuring company "bound by fierce devotion that puts mere family loyalty to shame", but Duke Kharash, the lupinal guardinal, is given the moniker of "Talisid's Shadow" because he is "the closest companion to Talisid, sharing the Celestial Lion's passion for the hunt as well as his love for the untamed wilderness. The two are nigh inseparable..." Let the Ho Yay commence.
Cat: A Little Game About Little Heroes explains that 1000 years ago, cats won a three-way competition between cats, dogs, and humans, thus earning the right and responsibility to protect the last-place entry (humans) from evil. Dogs also love humans and protect them, but resent the cats for beating them.
You will often see foxes and wolves paired as rivals; this goes back to the "beast epics" of Reynard The Fox, which featured Reynard and his rivalry between the wolf Isengrin. For a more modern example, well, how about, "Can't let you do that, Star Fox!"
In one educational Sierra textgame (Apple II era), wolves eat foxes.
Subverted in every respect in Ghost Trick. The black cat Sissel gets along incredibly well with the dog Missile and quickly makes friends with him. Also, he seems to have an aversion to hurting rodents. Might have something to do that for 99% of the game, he doesn't know that he is a cat.
Two Pokémon species, Zangoose (a mongoose) and Seviper (a snake), are natural enemies who attack each other on sight, to the point where their rivalry seems to be the only trivia ever mentioned in their Pokédex entries. Despite this, they can breed with each other.
There's also Heatmor (anteater) and Durant (ant). One attacks the other for food, the other retaliates in self-defence.
And in both cases, you can actually witness the jingoism in horde battles in Pokémon X and Y, where you'll fight four of one and one of the other, with the four ganging up on the one and ignoring you.
Averted in Touhou with the three Cat Girls, who are in friendly terms with other characters of species usually enemy to cats. The first, Chen the Nekomata, is the servant of Ran Yakumo, a Kitsune, which is related to dogs. The second, Orin the Kasha, is best buds with Utsuho, a Hell Raven AKA a bird. The third one is Shou Toramaru (actually a tiger), who is the master of the mouse youkai Nazrin.
Gunnerkrigg Court features Reynardine and Ysengrin, the fox and wolf of legend. While neither of them can really claim to be those animals anymore, Ysengrin was very upset to see Reynardine take the form of a wolf.
In Poharex, the dinosaurs have a mortal emnity with the Rakair, a species of evolved rauisuchians. They also hate humans, though to a lesser extent.
In Homestuck, Jade can't help but growl and bark at Jaspersprite when he starts meowing, because the latter is a cat, and the former, through a very complex series of events, has the instincts of a dog.
The cat/dog rivalry is inverted in Reynard Noir, where Cassandra Cat and the technically canid Slylock Fox have an on again/off again romance. However, speciesm is fairly rampant amongst the population as a whole, especially in the case of predator vs. prey species or humans vs. nonhuman. Sayings such as 'blind as a bat' are even regarded as speciest slurs.
Heffer's grandpa hates wallabies. The good news is, his eyesight isn't so good and he mistakes Rocko for a beaver. The bad news is, he's not too keen on beavers either. Cats and turtles are said to be mutual enemies, without much explanation, in the episode "The Big Question"/"The Big Answer." This rivalry exists solely for the purpose of creating tension leading up to the marriage of recurring characters Filburt (a turtle) and Dr. Hutchinson (a cat).
One episode shows Heffer — a steer who was literally Raised by Wolves — being sent out to "bring an elk home for dinner". He ends up dating one.
The Lion King features a lion/hyena rivalry, which actually reflects the reality of the African savannahs, to a certain extent. Though The Lion King inverts it, based on the old misunderstanding of their interactions. Newer research suggests that its the Hyenas who do the hunting and it's the Lions who muscle them away from their kills. Even newer research suggest that both sides play both roles when it suits their purposes, though lions still do most of the stealing.
My Gym Partners A Monkey. Here, the animals are sentient and speak and are humanoid (mostly) but the snake kid still fights with the mongoose kid.
Subverted in the "Rita and Runt" segments of Animaniacs in which Runt habitually goes into an aggressive posture/attitude at the mere mention of a cat, yet is too stupid to recognize that his best friend Rita is a cat.
Most of the Tom and Jerry cartoons fall into this. Jerry is chased by Tom who is in turn chased by Spike solely because they are a mouse, cat, and dog. Yet at the same time they are shown to get along with each other fine. In one cartoon where Tom throws Jerry out he starts to miss him and is glad when he is actually back.
Hanna and Barbera later went on to create Pixie and Dixie and Mr. Jinks (for The Huckleberry Hound Show), and Motormouse and Autocat (for the Cattanooga Cats show) which naturally have similar themes; the latter involving vehicles.
An American Tail uses the old Cats vs Mice rivalry as a metaphor for the rich vs the oppressed immigrants in the late 1800's.
In Bolt, Mittens tells Bolt that cats hate dogs - because secretly they want to be dogs. Throughout the film, she and Bolt echo cat/dog rivalry sentiments, addressing each other as Dog or Cat until their friendship grows.