In the Sonoran Desert, the Arizona bark scorpion is feared for its potent sting. It's the most venomous scorpion in the U.S., and a sting can cause agony for days, leading to hundreds of hospital visits each year. But the Southern grasshopper mouse has developed an astonishing defense—it can effectively numb its own pain receptors while doing battle, rendering the scorpion’s repeated stings painless.
CONTENT NOTE: This video shows a scorpion stinging a mouse in the face! Repeatedly! It gets a little intense just past the 2:00 mark, but the mouse turns out fine. The scorpion is lunch.
For more on this (or if you can't watch the video), check out KQED's article about the scorpion/mouse arms race, which features this particularly scary passage (emphasis added):
Commonly found in the Sonoran Desert, the Arizona bark scorpion (Centruroides sculpturatus) is the most dangerous scorpion in the continental United States. According to Keith Boesen, Director of the Arizona Poison & Drug Information Center, about 15,000 Americans report being stung by scorpions every year in the U.S. The worst stings, about 200 annually, are attributed to this one species. Its sting can cause sharp pain along with tingling, swelling, numbness, dizziness, shortness of breath, muscular convulsions, involuntary eye movements, coughing and vomiting. Children under two years old are especially vulnerable. Since 2000, three human deaths have been attributed to the Arizona bark scorpion in the United States, all within Arizona.
Check your boots, folks.