Rattlesnakes have thermoreceptors on the front of their faces called organs, which allow them to detect infrared radiation.
setae
pit
thermo
heat

Pit

Explanation:

Pit are one of the organs in rattlesnake that allows them to detect infrared radiation. The other organ that functions in a similar manner is their eyes.

The pit organ acts like a pin hole camera, allowing radiation to pass though its opening and eventually hitting and warming the back wall.

The ability to detect infrared heat radiation enables rattlesnakes to locate its prey in any environmental condition, especially in the dark. Rattlesnake's preys are usually warm blooded, hence, the relevance of the infrared heat radiation detecting pit.

Melanin- a large group of related molecules responsible for many functions so like pigment of the skin, hair and eyes

Carotene - pigments that are oxygen-free. Most are hydrocarbons (hydrogen and carbon ONLY) their colour varies from yellow to orange to red