Most of the issues I have seen from live rats is when the snake is not interested and left in there overnight. The same thing happened to my big bp and left no blood he even had the same trouble as yours.

My boa ate a 110 gram rat one time when he weighed 400 grams. The rat did not look that big in the store and when I saw him with it I was like uh oh! But he had a lump and was just fine.