All I can say is in my opinion it is bad practice to use Ferrets on rats,using the same ferrets on rabbets will make them harder to pick up and they normally kill more often.
Yes Molly they only get a little bite now and then,how would you feel if that one bite took snowies eye out ( it's happened to me ).It doesn't take many rating trips for your ferret to refuse to enter to rat.
I know because I did all that stuff when I was young, there was no one to tell me any different.
Yes it is good fun but Rats will F**k up a good ferret.