female rats biting each other!

Question
Hi there, i hope you can help! i have 2 female rats, about 12 weeks old, albino...gorgeous! from a pet store and apparantly sisters; one is biggest than the other though, she may well be the runt of the litter (this one is very docile and submissive and seems the intelligent of the two)

They get on ever so well, curl up to sleep in the hammock together, drink from the bottle together, groom etc. However, last night and today i've noticed the bigger rat biting the smaller one. THe bigger is alot more defensive and she's bitten me and my daughter before. I think this was due to her poor eyesight though.

The biting that she does to the smaller rat though seems ever so aggressive. She pulls on her fur and skin - its almost like a mother cat would carry her babies. But its not on the scruff of her neck its on her side, on her back - well anywhere really! the smaller squeaks and is very docile and passive but the bigger doesnt always stop. I've not noticed any blood drawn yet but it looks more than play fighting.

Please help, the smaller is lovely and i dont like the idea of her being hurt!

Many thanks!  

Answer
Sounds like typical young rat behavior.  They play fight, chase, pin each other down, you name it, they do it.  They usually outgrow it though. They should not bite you, though. When the rat bit you and your daughter, what were the circumstances?  What makes
you thinik it was due to not being able to see  well?