Dogs

Dogs appear regularly in Zappa's work:

On the cover of Absolutely Free an advertisement for a dog collar can be seen, with the slogan "Buy a Fydo. Fits swell!"
On the covers of Cruising With Ruben & The Jets, Just Another Band From L.A. and Ahead Of Their Time Zappa and his band members are depicted with dog noses. Illustrator Cal Schenkel did this as a tribute to the dog characters in Carl Barks' comic strips about Donald Duck.
In The Story Of Ruben & The Jets it is revealed that Ruben has three dogs: Benny, Baby and Martha. The names Martha and Benny appeared earlier on the artwork of the cover of Absolutely Free, along with Ruben's name.
A dog with sunglasses can be seen on the covers of Francesco Zappa,Them Or Us and of The Perfect Stranger.
Evelyn, A Modified Dog
Stink-Foot: a dog, Fido, is called to fetch some slippers and goes into an argument about the essence of Conceptual Continuity
Dogs can be heard barking during the intro of Andy
Nanook Rubs It: while Nanook is rubbing a chorus sings "Here Fido, here Fido...."
Cheepnis: "'Cause she just might box yer dog/She just might box yer doggie/ An' leave you a dried-up dog biscuit" (...) the people try to catch Frunobulax by calling "Here Fido, here Fido..."
Dog Breath, even though the term is also American slang for a person with very bad breath
Zomby Woof: "woof" is a sound associated with dogs
Honey Don't You Want A Man Like Me: "He had an Irish setter"

Specific articles about dogs

The Poodle Lecture
Dirty Love and Stink-Foot: "The poodle bites, the poodle chews it."
Hunchentoot and Cheepnis: "The monster which the peasants in this area call Frunobulax and apparently a very large poodle."
Food Gathering In Post-Industrial America: "as the denizens of New Perfect America dine on rats, poodles,..."