He does it when your pissing him off by hovering over him and sticking your hands in his face. These guys are pretty tempermental, the slightest leaf change can cause them to go into food strike. There really more for show over the mantel than a dog u can play with. But yeah, they get stressed over other things but mostly because of their owners messing with there stuff. If you want to handle it make sure you move your hands slowly and place your pointer finger between its front legs. he'll either climb onto your hand or over it with not much of a fuss. never come over top and crab its back.