Do eyes really turn black when they hunt?

The eyes of some predators do appear to turn black when they are hunting, but this is not due to a physical change in the color of the eye itself. Instead, it is an optical illusion caused by the dilation of the pupils.

When a predator is hunting, its pupils will dilate, or become larger, in order to allow more light to enter the eye. This increased light sensitivity helps the predator to see better in low-light conditions. The dilated pupils can also make the eyes appear to be completely black, especially from a distance.

In humans, the pupils will also dilate in low-light conditions, but they do not typically appear to turn black. This is because the human iris, which is the colored part of the eye, is relatively large. Even when the pupils are dilated, the iris still covers a significant portion of the eye, preventing it from appearing completely black.

In some predators, such as cats, the iris is much smaller. This means that when the pupils dilate, the entire eye can appear to be black. This can be a useful adaptation for hunting, as it can help the predator to blend in with its surroundings and avoid being seen by its prey.

So, while the eyes of some predators may appear to turn black when they are hunting, this is not actually due to a change in the color of the eye itself. It is simply an optical illusion caused by the dilation of the pupils.