he can also crawl backwards - it's mostly using his arms. when he's on his belly, his legs splay out like a frog's. once he learns to keep his legs in so he's on his knees, he'll be going non-stop... i'm happy to wait a little longer for a mobile z.
speaking of mobile, z learned to turn on the mobile in his crib. i think we'll need to remove it soon, as all the baby proofing websites say they should be gone after 5 months, or after they can reach it (he can't quite yet).