Three molecules discovered in spider venom may provide a new tool to probe how the receptors on sensory neurons work to produce pain. When researchers injected the purified toxins into the paws of mice, their limbs became inflamed and the animals reacted by licking them and flinching. Mice genetically engineered not to express the receptor, however, did not react when the toxin was administered, according to the study in the November 9 Nature. The peptides isolated from the tarantulas target the same receptor as capsaicin, the fiery compound in hot chili peppers. But unlike capsaicin, the tarantula toxins target the outside of sensory neurons and could be used to study neurons without destroying them.