It is unknown why this happens, but Toy Bonnie's eyes, particularly his pupils and irises, get smaller and smaller the closer he gets to the player. None of the other animatronics does this, and it is said to have some supernatural reasoning.

It is like his eyes contract, like that of an animal's, but, when a light is shined upon them, they remain the same. In the close-up of Party Room 4, his eyes can be seen smaller, and, once he is in the Office, they shrink even more.