The cat pupils on TikTok look so big because cat pupils have the ability to adjust automatically. A cat's pupils can automatically contract or dilate depending on the intensity of the light to adjust the amount of light entering the eye.

In low-light environments, cats' pupils will dilate to absorb more light and improve visual sensitivity. In strong light environments, cats' pupils will contract to prevent too much light from entering the eyes. The videos on TikTok may have been shot in low-light environments, so the cat's pupils look particularly large.

This ability to adjust automatically is a natural characteristic of cats, helping them to achieve better vision in different light conditions.