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A bird swallows a small red chilli and flies away . A person bites a chilli and reaches for water . The same fruit , two very different reactions . The burn comes from capsaicin , a chemical in chillies . Nerve cells in our mouths carry a sensor called TRPV1 , which opens when it gets hot . Capsaicin sticks to this sensor and sets off pain messages . David Julius and his team found the sensor , and that work was part of the 2021 Nobel Prize in Physiology or Medicine . Birds have this sensor too . In 2002 , researchers Jordt and Julius tested the chicken version . It still reacts to heat , but it does not react to capsaicin . So a bird feels real heat , but not the burn of a chilli . This matters for the plant . In a field study in southern Arizona , Tewksbury and Nabhan tested which animals ate small wild chillies . Birds , mostly curve - billed thrashers , ate them . Pack rats and cactus mice stayed away . The birds passed the seeds whole , and the seeds could still grow . Rodents chewed the seeds and destroyed them . Scientists think the burn may help the plant choose which animals carry its seeds . The most common chilli species was first grown as a crop in Mexico , most likely in central - east Mexico . So the next time a chilli burns your mouth , remember the bird . It eats a small wild chilli and feels heat , but not the burn . 
