It is perfectly normal when ferrets hiss.  My ferrets are, for the most
part, "mute" - they don't vocalize much at all... but, when Bart gets to
dragging Victoria around by the neck or ear, she hisses, too.  Believe
it or not, it's actually a sign of affection (in this case).  Victoria
actually likes the attention, and as soon as Bart leaves her alone, SHE
will badger him into doing it again.
 
Ferrets hiss for many reasons, but as long as there's no fighting with
blood or poop, they should be fine. :o)
 
Gary
[Posted in FML issue 4323]