The box turtle, for example, is really a tortoise. Living on land, they encounter all kinds of deadly mushrooms that grow to just the right height for them to munch. Consuming these toxins, the box turtles' flesh can become toxic as another deterrent to predators (when the shell just isn't enough). Many years ago, this possibility was well known by indigenous peoples. A number of eastern native tribes and nations had taboos against eating these tortoises, and just to be on the safe side we should too.