'Cause he kicked him.
Everyone was posing (reasonably) nicely for the picture, when the photographer's assistant started squeaking a toy to get the dogs to look at the camera. Which sent Moe into a complete frenzy, of course. Poor Santa held onto him valiantly, but--from the familiar way he was rubbing his side when all was said and done--I'd say Santa got some mad, crazy terrier paws in the gut.
But I'm sure Moe was just thinking, "Wow thanks Santa! I see you already got me just what I wanted, now let me down so I can go kill it!"
