deformed snail?

I recently bought 4 mystery snails from my local LFS. All of their bodies are pinkish and healthy looking except one... His shell is healthy but his body is brown and looks almost dried out and cracked, plus he has this funky little ball thing on the top of his head... I wonder if he has a tumor... Anyone know? I tried to get a pic but it didn't work I have to wait until he comes to the glass which will probably take forever... he moves a million times slower than the other guys and at one point I think he may have stayed in his shell for over 24 hours. What is up with this little guy?!?

I'll keep trying, he is definitely not cooperating. I feel really bad... Maybe it doesn't even bother him but it looks like it hurts, you know? I guess the only thing I can do is watch him, I don't want to bring him back to the store

I tried the green beans and he did eat it, so I know he is getting food at least. Still can't get a decent pic!