Oh bugger, I feel terrible then, I've been feeding him too small. No wonder he seems a bit 'small'! I'll get a small mouse and a rat pup tomorrow, and see how he feels about the rat pup when it's time for feeding. (I understand that he might be confused, so to speak, about the mouse to rat transition (or just displeased, haha))
Edit:
On another note, if you got a chance to see the video, is his breathing 'normal' for a slightly stressed (I'm certain he heard me approach) Ball?