I bought a pego rat from the store, because my other two has done nothing for the last two months. I new female i got on monday night and held her for a few hours and she seemed to be a sweet heart, on tuesday she gave birth to 10 pups, two days later when i was feeding her she nipped but did not brake skin, thin went on for a week, now she's okay with hold the babies moving the nest to clean, so maybe due to their bad eyesite she miss took your finger for food, or she just didn't want you in her cage with the pups. so just wait on making her food she if she bite after the pup are out of her cage. hope this helps you out