I have a boy that wags his tail to come out of the cage.  You can always
tell when he is gonna do it as he will stare at you first (you can feel this
stare from across the room!).  All you have to do is say, "Wag your tail,
Whatchamacallit!" and away it wags!  He also wags it in tubes.
 
My In-law's girl will also wag her tail if she goes into the space between
the speakers in the living room & you try to reach for her.  She is just
silly in the first place.  She will be under & inside the couch & when you
drag her out & tell her "bad girl" & send her on her way she runs as fast as
she can towards the TV & whips around & shoots you a dirty look & then
takes off again!  As if to say, "Damn hooman!".
 
We also see tail wagging in kit play a lot.  They seem to grow out of it,
tho.
[Posted in FML issue 2376]