Some people claim that the ferret learns, at this point, that they must be doing something wrong - biting you, and that they look at you as the 'mother ferret' and learn that this type of behaviour is inappropriate... There are three key problems with this argument.
The first is that, in reality, the mother teaches the baby ferret how to interact appropriately with other ferrets, not just with her. She does this, allegedly, simply by scruffing the babies, but as I mentioned above the ferret is behaving appropriately for a ferret. If you have more than one ferret, then he or she will already know that this nip was acceptable in ferret terms from social interactions with other ferrets.
The second is that we, as humans, use scruffing for more than just discipline - we scruff ferrets to give them medication, to check their teeth, to get them to hold still for a moment, or just to see them give a nice, cute yawn. How is your ferret supposed to know the difference between when you would like them to alter their behaviour, you want to give some medicine, brush their teeth, trim their nails or give them a kiss? Remember: as far as a FERRET is concerned, the above nip was perfectly acceptable.
The third key problem with this argumet is that it assumes that the ferret - a social animal - is incapiable of learning appropriate behaviour from non ferret communication. This is not true for social animals - they tend to learn how to behave in social situations and how to interact with other animals and humans. Given the opportunity, a ferret will learn how to do tricks (cues and commands are very non-ferret like) and interact with other animals (including the warning sounds of other animals which are not ferrets). They will learn how to respond to a cat or dog without having been taught appropriate behaviour by having that animal scruff them.
Personal experience: The dog.
Our ferrets all respond to the dog. She treats them as though they are her babies and will often protect them from visiting animals (and the cats). She will play with them and groom them, but when she has had enough, she will let them know to leave her alone. She does this not by scruffing, but by bearing her teeth at them. If they persist, then she will growl. If they continue to bother her, then a warning snap (similar to what a mother dog would do to communicate inapropriate behaviour to a puppy) ensues. The ferrets know when the snap is coming, and tend to bugger off at that point. None of these signals are "ferret language" but as adaptable social animals, the ferrets have learned to understand the dog's signals, and what behaviour the dog deems appropriate at any given time.Personal experience #2: the cats
The ferrets LOVE to bug the cats. They love it. They giggle when they get a reaction, and often feel the need to 'move' the cats when one is sitting comfortably on a chair. Most of the time, the cats will get alarmed and move (cats tend to have poor social skills. Only our most social cat has learned to differentiate between happy ferret giggling and aggressive ferret who wants to eat the cat behaviour). On occasion, when one of our cats is feeling particularly grumpy and does not wish to indulge the ferrets with their favourite game, the cat will hiss. If the ferret persists (which they often do), then the cat will proceed to make and angry, agitated 'roar/growl' which the ferrets rightfully understand to mean "piss off or I WILL hit you". The ferrets back off at this point. Again - this is not "ferret speak" yet the ferrets understand the limits that the cats have setPersonal experience #3: Deaf baby ferret.
How on earth do you teach a deaf ferret not to nip? Why, scruff them, of course. Well, fortunately, this little guy doesn't really nip... much. He will nip your foot when you are ignoring him and he wants a treat or you to play. No amount of scruffing or scruffing and dragging seemed to help with this behaviour.. so what did we do? Started ignoring it. Scruffing gave the ferret what it wanted - attention. Walking away or going about your business and acting as though nothing happened did NOT give the ferret what he wanted. He quickly learned to scratch the foot when he wanted something, and we rewarded this behaviour with treats and attention.Personal Experience #4: the perpetual nipper
Though baby to train - she would ALWAYS nip everyone ALL THE TIME... except, for some reason, she shortly stopped nipping me... why? Everybody else employed the scruff or the scruff and drag only to get nipped again the minute that they were released. Scruffing until she yawned worked sometimes, but mostly when there was another distraction which would cause her to charge off to investigate that strange sound or new item. To this day, she will still nip my other half, but not me. At first, I explained this by the lack of reaction that I would give - no jumping or twitching when nipped, no fear, but the nipping persisted even once the only reaction that he displayed to being nipped was to scruff the ferret. I had a slightly different approach - ignore the nips and act as though they didn't happen. A bite on the face meant that the head would be turned away and I would continue to kiss the ferret on her head until I was done. Nip on the foot for attention meant absolutely no reaction. Persistent nips when I was lying on the ground were met with no reaction. Walking up to me and tapping my foot, licking my face, jumping or walking on me all received enthusiastic reaction - praise, treats, attention. I started to wonder whether my lack of "scruff and drag" which seemed to cause her to get MORE exited (I often wondered whether she interpreted this as play or just felt that any attention was worth it) is in part responsible for this difference in nipping behaviour. One final addition: I can play wrestle with this ferret with my bare hands with no problems - she is one of the most gentle ferrets that I have ever met when I comes to playing with me, but my other half can barely even carry her on a walk or hold her without her attempting to nip him at least once. 
