Griffin started clapping about a week ago. The 12th of April, to be exact. We think it might be because he saw another baby (Sage) doing it on Friday, but that's unconfirmed. Regardless, he spent much of Saturday happily clapping at the slightest musical stimulus. I put on a mix of CDs for him and he had a good time. He's not doing it constantly now, but does it every now and then, usually linked to either happiness or music.