Okay - let's start with the disclaimers. First, he's swinging so most of these are a bit blurry. I could have used the flash, but he doesn't like it.
Second, he sometimes accidentally scratches himself so he has on some little mittens. It's not a dance costume.
And third, he doesn't really know what he's doing. He likes music and his arms are flailing, but there's not much connection between the two. It's pretty random. Maybe it should be jazz arms rather than jazz hands.
As soon as he knows what he's doing, I'm teaching him to do Y-M-C-A. He's a natural and already has the Y.