Cooler snakes respond more strongly to infrared stimuli, but we have no idea why.

The pit organ defining pit vipers (Crotalinae) contains a membrane covered with temperature receptors that detect thermal radiation from environmental surfaces. Temperature is both the environmental parameter being sensed and the mechanism by which the pit membrane detects the signal. As snakes are ectotherms, temperature also has a strong influence on neurological and locomotor responses to the signal.