Daniel Heuclin / Western diamondback rattlesnake (Crotalus atrox) tasting air, in habitat, Arizona, USA, October. Controlled conditions

Daniel Heuclin / Black-tailed rattlesnake (Crotalus molossus) tasting the air, Arizona, USA, September. Controlled conditions

Daniel Heuclin / Black-tailed rattlesnake (Crotalus molossus) tasting the air, Arizona, USA, September. Controlled conditions.

Daniel Heuclin / Southwestern speckled rattlesnake (Crotalus mitchellii pyrrhus) tasting air, California, USA, October.

Daniel Heuclin / Southwestern speckled rattlesnake (Crotalus mitchellii pyrrhus) coiled tasting the air, California, USA, October.

Daniel Heuclin / Arizona black rattlesnake (Crotalus cerberus) tasting air and rattling tail, Arizona, USA, September. Controlled conditions.

Daniel Heuclin / Arizona black rattlesnake (Crotalus cerberus) tasting air and rattling tail, Arizona, USA, September. Controlled conditions.

Lynn M Stone / Western Diamondback Rattlesnake (Crotalus atrox) on rock with tongue extended, Phoenix, Arizona, USA. Non exclusive.

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli) eye and pit sensory organ, Mindo, western slope of Andes, Ecuador

James Christensen / Ringed Tree Boa (Corallus annulatus) showing prominent loreal pits for heat sensory, Colon, Panama

ZSSD / Southern Pacific Rattlesnake (Crotalus viridis helleri) coiled up showing head with sensory pit organ, North America

ZSSD / Red Rattlesnake (Crotalus ruber) portrait showing eye and pit sensory organ, native to North America

ZSSD / Brazilian Lancehead (Bothrops moojeni) snake showing eye and pit sensory organ, native to South America

ZSSD / Brazilian Lancehead (Bothrops moojeni) snake showing nostril and pit sensory organ, native to South America

Pete Oxford / Timber Rattlesnake (Crotalus horridus) showing heat sensitive pits, northern Georgia