well I peeked in.. and no, doesn't look like it left a lump at all. It was a small/med mouse.. the only size the pet store had at the moment. Which I guess is a good thing, now that he ate. It wont stress his system out too much, and if he wants I'll offer him another small/med sized one again on friday. if he doesn't eat, I'll just hold onto it until the following week.. (love that spare 5 gal tank for those extra feeding mice).