So i have had a couple female rats for a few months now. they have been really nice not mean easy to take care of. So i have been thinking about breeding them to save a little money since i have to drive about 30 mins each way to get rats for my snakes. So about a week ago i bought a male rat from the same place so they can start their "business". Well last night while i was sleeping i heard some commotion going on in the rat cage but didnt think much of it since at night ( with my rats anyways) they are crazy and loud and play, yell and destroy their cage. When i went up to my room this morning to check on them their house was up side down and there was my favorite rat laying there in the middle of the cage dead. Her head was shredded into pieces. couldnt even tell the head was a rat. body was all still intact, and the other female and the male were in the corner scared..... So is this a common occurance for rats to kill each other? i would like to think its not . what do you guys think happened?
thanks

Christian