Yes, I said it CAN hurt them. Not all have had a problem with live, but I, from personal experience, have. Even when I didn't LEAVE the rat in the cage without being watched ( i would never walk away).
Sometime a wrong strike thought can still leave the rat plenty of biting room until they are squeezed to death. Either way I don't think you'd want any wounds whether they be big or small. I just think giving that this person has little to no experience....try f/t first if they want to see if they'd even eat.