Brian, I go by the rule that if it's not hard enough to be uncomfortable then
nibbling on fingers/toes is ok. My male likes to do this but just mouths and
never bites down or even applies pressure. My female doesn't do this at all.
Younger ferrets do need to know how hard they can chew on people and as long as
they can be taught what pressure is ok then I don't see any reason to stop the
behavior. If it makes you uncomfortable though then you can just consistently
say "no!" and she should get the idea.
 
[Posted in FML issue 0638]