Toe-biting Possums

Many brushtail possums have a toe-biting habit. When I was on holidays in Tasmania a few years ago, one of the local possums (named Rufus) greeted me in the following way:

Rufus toe-biting - Cradle Mountain, Tasmania 8/9/2008

I haven't worked out what the motivation for this is.

The majority will advance menacingly towards a person's foot, lightly nip at the big toe then run away. Some, however, will merely sniff at a toe. Very few will bite hard. Some possums never toe-bite at all. Ginger, our first possum, was like this. She would occasionally climb a person's leg, but never toe-bite.