Graham, when living in Brunei, I had a nurse shark of about 60 pounds take a liking for my flipper. It took hold and swam, dragging me for about 20 meters before the fin was ripped from my foot. Rather funny now, but at the time I discovered poo sticks to a wet suit!!
The power was scary, and so were the head shakes. I still have a damaged knee to this day, 20 years on!!