I've been nibbled at by a lot of mice but only one broke skin. She got dropped, the cat is always waiting closeby just in case one jumps or gets dropped. I was recently given some completely unsocialized gerbils, adults and babies and was suprised none of them tried to bite. I've been bitten by rats a couple times, which is why I don't breed them as of yet, I want to start with babies so I can handle them young. Rat bites bleed like mad!