And There Was Much Rejoicing: The dogs have a song about another dog from their lab. It ends with "His name was Kiff, he was black and white/He was burned to cinders—serve him right." Subverted, since Rowf and Snitter actually seem to miss Kiff and often mention him
Doom Magnet: Snitter literally believes himself to be this, suggesting that they cannot kill him because if he dies all the humans would die, too.
Everyone Has Standards: Driver Digby is generally a selfish, amoral bastard. However, he's disgusted and angered when he finds out that Snitter's owner didn't die, and his sister still sold Snitter to A.R.S.E. Digby's anger over this surprises even himself.
Eye Scream: The hunter pointed his rifle at just the right angle, although we see nothing more than him clutching his face with blood everywhere.
Family-Unfriendly Death: Oh so very many. The tod is killed by hunters, both dogs are strongly implied to have drowned, a man is shot in the face with blood splattering everywhere, and a hunter is killed by a long fall and his corpse is eaten.
For Science!: Most of Dr. Boycott's animal testing. For example, in one experiment, cats are forced to wear hoods that constantly cover their eyes and ears. The purpose of the experiment is to find out what happens to cats who are forced to wear hoods that constantly cover their eyes and ears.
Fun with Acronyms: The animal testing laboratory is called Animal Research: Scientific and Experimental, or A.R.S.E.
Gallows Humor: Snitter has a dark sense of humor. It irritates Rowf.
God Is Inept: Rowf believes that the star dog gave the world up as a bad job.
Grey and Gray Morality: When the story starts it seems quite clear that the baddies are the whitecoats and the men with guns, while the goodies are those who show sympathy to the dogs. Later, as the characters become more developed, the "baddies" begin to appear more human, reasonable and even nice in their own way, while the "goodies" show signs of shallowness or hypocrisy. (See Humans Are Bastards.)
Humans Are the Real Monsters: Played with. The "Whitecoats" certainly qualify here, even to the point of being Cthulhu-esque, but most of the humans are three dimensional and are only after Rowf and Snitter because they killed sheep and eventually a man. Completely averted in the case of Snitter's idea of "Masters," whom he almost deifies.
Serious Business: Geoffrey Westcott takes the fact that the dogs broke into his car to steal some food a bit too seriously, and goes on a one man crusade to try and hunt them down.
Shell-Shocked Veteran: At the research facility Rowf was forced to swim around in a tank of water until he couldn't swim anymore and drowns. He would then be taken out of the tank, revived and forced to repeat the whole process over again. The experience has understandably left him with a crippling fear of water.
This Is a Work of Fiction: In the foreword, Adams explains that the unsympathetic characters are entirely fictional, but the sympathetic ones are usually real (though many of them already moved from the Lake District or died by the time the novel was published). Also, Animal Research: Scientific and Experimental does not exist, but the experiments described were all carried out in reality.
Blatant Lies: In the film, while Rowf and Snitter are running from the humans, the tod offers to distract the humans so they can get away. He ends up getting killed in the process, and Rowf and Snitter are very aware of it, but assure each other that there's no way the humans got him, because he was too clever. They are both quite aware that this isn't true.
Bolivian Army Ending: The movie ends with the two dogs swimming out to sea trying to reach an island. Just to increase your doubt in either direction further, the last shot is of an island, while the music for the credits is a song about dying and going to Heaven.