Snakes are seeing in the closest to visible specter IR IIRC. Also they have evolved a lot of other sensory mechanisms to detect pray - sounds, vibrations, taste
Wow, so instead of a photochemical or photoelectric effect, it's actually literally a heat sensor - as in, radiation from the environment heats the interior of the heat pit (which is cooled by the snake's blood to maintain a baseline) and it is this change in temperature that is detected?
I wonder if the ribbonfarm guy could use a variant of this for his pixel scanner thing?
They can sense radiation between 5 micrometers and 30 micrometers.