Stereo, or 3D, vision is what enables humans to gauge the depth and distance of surrounding objects. The right and left eye capture slightly different images and send them to the brain, which merges them and then calculates the proximity of everything in the vicinity. The ability, which requires an intricate network of neurons and lots of processing power, can also be found in a select group of animals like cats, horses, owls, and sheep, as well as one insect — the praying mantis.