Pythons and pit-vipers are equipped with heat-sensing pit organs that allow them to detect warm-blooded prey by sensing the temperature difference between their prey and the surroundings. These pit organs allow them to hunt even in complete darkness.

In pythons, the pit organs are located along their upper lips and often the lower lips as well.

In pit-vipers, the pits can be found between their nostril and eyes.

Top: Reticulated Python - Canon EOS 30D with Tamron 90mm 1/100sec at f8, ISO 250, Flash fired.

Bottom: Wagler's Pit Viper - Canon EOS 10D with Tamron 90mm 1/200sec at f11, ISO 100, Flash fired.