lol, yes, sometimes they do this, well mine does at least, the snake probably got confused and smelled the rat on "him", and decided to go for it, somehow not noticing hes biting himself, or maybe he thinks the rats biting him and that he has the rat? im not sure, but i kinda freaked out the first time mine did that too, but after a minute or two he realized what was going on and went back to the rat