He sees the toothbrush coming and is instantly flat on his face to avoid it.  

When I don't fight him right away, he's curious why not and discovers I have the camera out.  

I haven't gotten the shot yet, though, so I hold up the toothbrush again and he whips back into position.  Over and over again.  Camera, curious.  Toothbrush, face down.

I get the shot in the end, and I get his teeth brushed, too.