Cats

Cats often appear as a theme on.

Father O'Grady mentioned brown cats twice.

owned a junkyard cat that he named Jack Bauer. Jack Bauer was born in a pool of gasoline on a piece of rusty scrap metal and is indestructible. (Bums: Making a Mess All Over the City)

Cats live outside of Charlie's apartment due to the cat food left in the apartment, which as Charlie describes, is to attract cats who kill the rats. The cats meow quite a bit, understandably, so Charlie and Frank have to drink beer, huff glue and eat cat food to induce a feeling of sickness and tiredness. (Dennis Reynolds: An Erotic Life) 

A neighbor of a critic who insulted Paddy's Pub had a pet cat (who had diabetes) which the Gang kidnapped. (Paddy's Pub: The Worst Bar in Philadelphia)

Charlie had so much trouble with cat noise that he invented kitten mittens. (Paddy's Pub: Home of the Original Kitten Mittens)

Dee bought a cat but it accidentally got trapped in her wall. (Mac and Dennis Break Up)

Maureen Ponderosa self-identifies as a cat. (McPoyle vs. Ponderosa: The Trial of the Century)

Frank describes serving "Cat Soup" and human appendages to his sweatshop workers in Vietnam. (Making Dennis a Murderer)