Turtles are always rumored to have a "Death Grip", if they grab you, they won't let go sometimes until death.
Here are two captured Logger Head Turtles, a 29 lb one on the left and a 20+ lb one on the right.
When they got close together, they started snapping and biting at each other.
The 29 lb Logger Head Turtle has the smaller one in a "death grip".
His bite was so powerful we could hear the skull bone cracking. After about 15 minutes, he let go.