"The term is gape, the size of the mouth opening," explained Jayne. "Most snakes are limited to prey they can swallow whole. It's a little mind-boggling, but prey size limits must be rethought. We don't know what the upper limit is now."
There is another benefit to preying on soft-shell crabs, according to Jayne. Gerarda prefers freshly molted crabs which have very little mobility. "That means they can feed with impunity. There's almost no cost." Other benefits include being able to consume prey more quickly.
In contrast, Fordonia eats primarily hard shell crabs and can be injured while capturing and swallowing its prey. "Eating any hard-bodied animal is a task. It's a very tough chore for a snake."
Jayne said the take-home message is that you shouldn't jump to conclusions about vertebrate behavior by relying solely on anatomical evidence. The research was funded by the National Science Foundation.