I saw a video clip once of an alligator snapping turtle that was doing the open-mouthed threat while someone was holding it. A second person reached a broom handle out and into the turtle's bite range. Half the broomstick promptly fell to the ground, and the turtle didn't even seem to have spent any real trouble splitting it neatly in half. I'd be nervous even getting a LEG near an alligator snapper, let alone my precious hands!!!
Also when I was in first grade, we had a class turtle as a pet. I was told it was a box turtle, but now that I'm older, it didn't look like any box turtle I've ever seen before. Anyway.
One of the kids was antagonizing it, poking it in the eye and neck whenever the teacher wasn't looking to make it draw it's head back. Needless to say the turtle finally got fed up about the same time I did. The turtle bit off the tip of the kid's finger(and I think it ate it) and I threw a book at the kid's head.
I got suspended for a week - but I never saw the turtle again.
Point being - I'm keeping all of my digits VERY far away from turtles of ANY kind.