The rat which was eaten simply died, for what ever reason. I wouldn't suggest feeding the remaining rats to your animals unles you are sure the cause of death isn't poison. I have seen this happen too. I bought some rats during the winter and one night the heat went out. The next morning one rat was missing his head (it had been chewed off!). I figure this, a dead animal will attract bacteria and become a health hazard within hours. The rats figure better to eat it and get protein then be stuck in a cage with a rotting stinking bacteria magnet.