Now that I think of it, the worm's freezing up may have been an instinctive reflex. They could never hope to outrun a snake but they might have a small chance of avoiding detection. Of course that would only apply in the soil and earthworms likely lack the ability to distinguish black ground from tan aspen. That and snakes do hunt primarily by sensing vibrations, which may also explain why she was tasting the air around them with her tongue before she actually started taking them.

I have to say, studying these fascinating creatures is more than half the fun of owning them.