Raising Boys, Part 2

A while back I clipped a Garfield cartoon and put it in Matt's box of mail on my desk. The dialogue goes like this:

Liz: Jon, when was the last time you cleaned your oven?
Jon: I didn't.
Liz: EVER?!
Jon: The manual said it was self-cleaning.
Garfield [smugly]: We're bachelors, baby.

So last night we had this conversation:
Matt: [picks up cartoon]
Me: Did you see that?
Matt: yeah.
Me: Hahahaha, wasn't it great?
Matt: Uh. . . what exactly does it mean if an oven is self-cleaning?