When teaching ours that you can't bite humans as hard as other ferrets,
I do two things. First, when they bite my hand too hard, I force open
their mouth (gently) with my other hand and say 'no' or 'not so hard'.
This is pretty effective. The other method is to scruff them when they
are biting too hard and hold them down for a few seconds and say 'no'.
Neither method is too rough, but the scruffing and forcing the mouth
open are usually pretty clear signs that what they are doing isn't
good, and they've all learned pretty quickly.

Jeff
In Memory of Neo
Caring for Trinny, Morphy, Baby Girl, and Luna 

[Posted in FML 5950]