Dancing
  A happy ferret will "dance," flinging himself about on all fours
  with an arched back.  Clucking is common too.  Dancing or just
  careening into walls or bookcases is not at all uncommon, but
  ferrets seem to just bounce off of such obstacles.  Unless they
  actually injure themselves, don't worry about them; they're having
  fun.

Occasional sneezes
  If you crawled under bookcases and couches, you'd sneeze too.  Also,
  ferrets have a pair of scent glands near their chins, and sneezing
  can be a way of forcing some of the scent out so it can be rubbed on
  something.

"Reverse sneezes"
  These sound almost like asthma, about the same duration as a sneeze,
  and often occur several in a row, maybe after the poked her nose
  somewhere dusty.  They don't look or sound like a cough.  You might
  see the ferret's rib cage or body move once or twice a second with
  the force of the inhalation.

Sniffing/wiping/licking the rear
  This is a normal thing to do, especially after a bath.  It helps
  spread the ferret's scent around.

Licking urine
  It's not uncommon for a ferret to take a few laps of urine, its
  own or another ferret's.  Nobody's really sure why they do it, but
  it won't hurt them.

Hiccups 
  Hiccups are not uncommon, especially in young kits, who sometimes
  seem alarmed by them.  A comforting scritch, a drink of water, or a
  small treat [6.3] can help.

Tail-wagging
  For some reason, many ferrets wag their tails quickly when they have
  their front ends in a tube or under a rug and they see something
  interesting (a toy, a sock, another ferret) at the other end.  It's
  a normal sign of excitement.

Tail puffing
  A ferret's tail will bottle-brush when he's excited or upset.
  He's not necessarily frightened.  He'd have to be really
  worked up for the hair on the rest of his body to stand up, though.

Ear suckling
  Often ferrets will suck on each others' ears, and sometimes even
  cats' or dogs' ears, especially when they're sleeping.  It's
  probably a lot like thumb-sucking in humans, and nothing to worry
  about as long as the one doing the sucking is eating well and the
  other one's ears aren't getting sore.

Licking soap
  For some reason, many ferrets love to eat soap, stealing it from
  the bathroom or even licking the tub.  A little bit of soap won't
  hurt your ferret, though it may give her diarrhea.  Don't give it to
  her as a treat, of course, and try to keep it out of her reach, but
  it's nothing to panic about unless she manages to eat a lot.

Summer weight loss, in males
  Normally, weight loss is something to be concerned about [9.7], but
  many males lose a fair bit of weight, even as much as 40% of their
  bulk, in the summer and gain it back in the fall.  It's mainly
  preparation for breeding, but it's common in neutered males, too.
  If your ferret seems otherwise healthy and happy, don't worry.