I, too, have seen the ferret in the movie and think the sound he made were
extremely exaggerated.  I think the idea behind that was to show the
character played by Doogie Howser communicating with the animal
telepathically.  Perhaps the ferret's response is what you would hear if you
could talk to your ferret.  It is somewhat analogous to the sounds heard by
dolphins.
 
Go ferrets!
[Posted in FML issue 2123]