I have had the same happen to a few of the rodents I have purchased. I really don't know what causes it, ear infection, blown ear drum, genetic trait, or whatever but it never has affected my snakes when they eat. As long as the rat goes through its normal schedule I would keep it alive and let it breed. On the other hand if they're sores present I would just put the rodent out of its misery and dispose of it without ever feeding it to my snake....just a suggestion