If you got stung by a bark scorpion, you would probably howl with pain; their stings are said to be among the most painful of all insect attacks. But tiny grasshopper mice routinely eat bark scorpions,unfazed by repeated stings. It seems, in fact, that grasshopper mice are completely immune to scorpion venom. They don't feel it at all.
Video here, and some analysis of the biochemistry behind this resistance.