The Arizona bark scorpion is the deadliest scorpion in the continental United States. But the Southern grasshopper mouse happily munches on the scorpions. How? The scorpion's venom actually triggers the mouse to numb itself to pain.
From KQED Science:
The scorpion venom contains neurotoxins that target sodium and potassium ion channels, proteins embedded within the surface of the nerve and muscle cells that play an important role in regulating the sensation of pain. Activating these channels sends signals down the nerves to the brain. That's what causes the excruciating pain that human victims have described as the feeling like getting jabbed with a hot needle. Others compare the pain to an electric shock. But the grasshopper mouse has an entirely different reaction when stung.
Within the mouse, a special protein in one of the sodium ion channels binds to the scorpion's neurotoxin. Once bound, the neurotoxin is unable to activate the sodium ion channel and send the pain signal. Instead it has the entirely opposite effect. It shuts down the channel, keeping it from sending any signals, which has a numbing effect for the mouse.