I did a little bit of research in the forums here and it seems that most of the time, the tortoises associate a person with food and that's why they may bite. I do know the Aldabra tortoise Mzee (who is well known for his friendship with the hippo Owen) will give his friend love bites [http://en.wikipedia.org/wiki/Owen_and_Mzee]. Do other species like the Russian tortoise do this as well? Just curious!
Thanks!