According to Jim: The Cat Came Back

Cheryl's 15 year-old cat Mr. Feeney dies and she wants Jim to bury it on the backyard, but Jim desperately wants to go to the Bears game. He sticks the cat in the garage freezer, planning on burying it after the game, but Cheryl finds out before he comes home. She is hurt that Jim doesn't listen to her nor care about a cat that has been longer with her than anything in her current life. Jim, feeling guilty, provides a proper funeral for Mr. Feeney and gets her a brand new dog, which she doesn't like very much at first, but starts to accept it later.