Never have seen this before (that is, with other children), but my quirky, spunky, hysterical daughter, Miss Woo Loo, does this bizarre thing with her fingers sometimes when she's enjoying a yummy smackeral of something! She doesn't manipulate the fingers of one hand with the other, no, her fingers just twist and "clip" onto each other on their own. I think it's so strange. She thinks it funny that I react to it. She's one-of-a-kind, that's for sure.