Of course nobody is saying this WILL happen, but the possibility of serious injury is VERY REAL!. I've seen some bad injuries from this myself many times over the years, not to mention when this DOES happen, it often frightens the snake into associating future mouse scent with it getting hurt, and then can be extremely hesitant in taking them afterwards, and sometimes leads to the snake refusing them completely.
Also, freezing kills all parasites within the rodent prey, and is therefore safer for the snake to ingest. If you DO offer it live rodents later on, I would suggest "whacking"(killing) them first, this way, they cannot bite the snake.
best regards, ~Doug

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"Better to be silent and thought a fool, than to open mouth and remove any doubt!"