How does a rattlesnake detect heat?

Like all pit vipers, rattlesnakes possess notable heat-sensing pits. Behind each nostril of a pit viper, under a line that would connect the nostril to the aprorpos eye, is a loreal pit. These pits are what detect temperature, and effectively.

Additionally, thermal heat is visible to rattlesnakes: organisms have a unique temperature and are warm, thusly having "heat images." Heat images are correlated to size: the larger the organism, the larger the image is.