I work at an emergency clinic for animals.  The other night someone came in
with a ferret that they thought had broken its neck.  The ferret was playing
with one of those ferrets tents and had gotten stuck between the wire
support frame and the canvas.  The ferret had to be removed from the tent
by the owners and went into siezures upon removal.  Fortunately, the ferret
"only" received a bruised spinal cord and made a full recovery by morning.
The point--while your ferret is playing with *anything*, keep an eye on the
ferret to make sure something like this doesn't happen.
[Posted in FML issue 2411]