Our babysitter does these Franken-drawings with my kids. You fold the paper in thirds and one person draws the head and feet and the other person draws the mid-section of body. The idea is that neither sees what the other has drawn, other than the bit that connects one section to the next. The result is a really silly composite.
Our friend Cory (aka Momfilter secret weapon), just informed us that these drawings are actually called exquisite corpses and were invented by the Surrealists. The one below was done in 1927 by Man Ray, Miro, Morise, and Tanguy.