You also didn't give us a sense of the actual size, but in the past, once in a while I've seen a snake defecate some fur-laden material- you can actually see the swirls of thick fur in it- obviously it was more than they could digest- & btw, I don't recall this ever happening when feeding mice- only when feeding rats, & their fur is much more coarse (& apparently hard to digest). I wouldn't worry about it- chalk it up to just another snake-prank.