Compositing question

[desideriascott]

So i was watching spongebob today and i noticed in his pineapple house he is usually sitting on his recliner seat which is a flat object/drawing ,my question is is the chair two layers because when he sits down he is plush into the seat or well how is this technique done meaning having a 2d character interact with and object such as a chair under a table ,inside of a car sticking a head out etc. i hope i made this question clear enough