>Both my ferrets did this although not always the same location.  Eventually
>by observation we reached the opinion that they were finding the main veins
>in various locations (wrist, elbow, neck) using their tongue to track the
>heat and then biting.
 
I have a different (and slightly less disgusting) theory:
We've watched my two ferrets groom each other, and they usually lick lick
lick BITE each other, and I guess it feels good to them.  Once in awhile,
one of them will wake me up by doing this, and if I stroke and pinch their
skin (around the scruff, side of the neck, along their back) they start
yawning and licking.  I'm pretty sure they like it.
 
The other option is that they don't like to take a bite out of your arm
until they've cleaned it up a bit :)
 
[Posted in FML issue 1646]