However, that does not necessarily mean that they cannot detect what is going on around them – they just use different techniques. For example, pythons and boas have sensory pits on the scales on their lower and upper lips and these can detect movement on the ground by picking up vibrations.
These pit linings are also extremely sensitive to infra red radiation and act as heat receptors that are very efficient. This heat sensing apparatus is the most sensitive of any animal. Even at night, the receptors detect changes of less than 0.0001 degree Celsius.