Hmm, a lump ?

I don't know, is it really prominent ? Can you move it around gently with your finger, or is it solid in one place ?

I'd be worried it was a tumor of some kind. I think I'd be at the vet ASAP, just to be sure. If it turns out to be nothing that's fine, but if it is serious, the longer you delay, the harder it will be to have the breeder correct the situation with a refund or a new snake.

Gale