I really had to chuckle when my two were facing each other down in the
ferret tube the other day.  Those little tails shudder, vibrate, and twirl
wildly (even so far as to thumping) usually just before they are lunging
forward to attack, or just before they madly back up.  I don't know exactly
why, just that tail wagging occurs only when they are very excited.
 
Every day is fun with ferrets!
[Posted in FML issue 2626]