While playing with a butterfly, it says "butter! butter!"
While playing with a ladybug, "lay, lay, lay!"
While playing with a caterpillar, "cater, cater!"
Also, while playing with a pile of river rocks we bought at the craft store, he says "ahhh!" for each one jumping off a ledge. They are rocks playing Wipeout. I am pretty sure that in M's mind they are smacking into the big balls and then splashing down into the water. He also sometimes does the announcing, utilizing such phrases as "oh, that's gotta hurt!" and "oh man!"