Here's one Carla:
 
Q. Why do ferrets only wag their tails while in enclosed spaces such as
   tubes, and usually just before pouncing?
 
A. While hunting underground prey, ferret ancestors wagged their tails
   rapidly, hitting the sides of the tunnel and setting up a sonar like
   vibration.  The echoes coming back would tell the ferret how far away
   the prey was for the final pounce.
 
Linda Iroff
Oberlin OH
[Posted in FML issue 2949]