Mara, our small and stocky rescue girl, is a biter. In the 17 or so years we've had rats, neither The Mr. nor I have ever been bitten so much. She's bitten more than all our other rats put together. Some of it we've learned to mitigate-- make sure not to startle her, don't smell like food, the usual stuff. What breaks my heart is that she's started biting just because. Tonight, for instance, I'd just finished giving Mara and her sisters some treats during out time on the bed. They were all cheerful and zoomy, when out of the blue she lunged at my hand, sinking her teeth into my finger and yanking repeatedly, her whole wee body shaking with effort. The Mr. picked her up and put her back in the DCN so I could go and wash my hands, giving her a brief "time out." After about ten minutes, we let her back out. She comes up to hang out on my lap, and grabs on to my other hand teeth-first. Back to the DCN she went. We've never hurt her. We wash our hands before handling her. We don't pick her up unless there's a darn good reason, since she's usually perfectly happy to climb straight up us or to hop into a housecoat sleeve. She's been really good for the past few days, getting better at being gentle (licking is okay, chomping is not). Today, though, she's all teeth. Over the past few months she has also attempted to protect HandRat from FootRat (I was scratching my foot and she chomped on my big toe, possibly thinking it was attacking my hand). We both have numerous marks from getting bitten out of the blue. She's never bitten when picked up. She didn't bite the one time we took the bunch to the vet. We know some of the triggers, but not all. I don't know if it's hormonal, neurological, or something else. The vet seems to think she's got some PTSD from when she and her sisters were taken from their home. It was a hoarding situation and I believe the police may have been involved. She's a red-eyed Himalayan, so her eyesight isn't too good to begin with; there's a chance it may be worse than usual, since while her sisters sometimes do the head-weave thing, Mara does it a LOT. We don't put hands near her when she weaves, since we know she's nervous. Elsa and Della have adjusted just fine. Della's still occasionally skittish, but she's only ever attacked the wet sponge that was invading her home (she decided to scale me and climb back in while I was cleaning-- sponges are not her friend). Elsa is a people-person and loves attention. No worries on that front. That's part of why we think there's something psychologically or neurologically wrong with Mara. We're not giving up on her, but we're not sure what to do. Does anyone have any experience with sudden, unprovoked biting? Would it be worthwhile tracking the behaviour to see if it's cyclical and possibly hormone-related? How can we help our tiny ferocious muffin become less hazardous to our hands?