Mark Tatulli seems to enjoy not just using his comic strip Lio to present his unique brand of humor, but to play with the very concept of comic strips itself. Today's single panel sequence is an excellent example of that.
Lio opens a can of tuna, and attracts every cat in the neighborhood. And since Lio's neighborhood is the comics page of the newspaper, that's where the cats come from. (click on image to enlarge)
From left to right we see Mooch from Patrick McDonnell's Mutts, Bill the Cat from Berkeley Breathed's Opus, Bucky Cat from Darby Conley's Get Fuzzy, and finally Garfield from Jim Davis' eponymous strip. Strangely missing is Lio's pet cat -- but perhaps that's part of the joke.
Breathed created Bill the Cat as a satirical version of Garfield, so it's interesting to see them both in the same panel. And speaking of Bill, to call a character back from a retired strip -- that must be some powerful-smelling tuna!