Marc started singing Old Macdonald to Seth when he started this, and that combined with a toy calmed him down. He'd get the occasional "No." or "uh uh" if he was going to hurt himself. But other than that he was fine. You are right though it is something you want to try and nip in the bud. We also used to do peek a boo to get his attention.

*hugs*
Cailin