Perceptual illusions usually are harmless, in fact, we may find them amusing. O

Illusions occur for several reasons:
Normal perceptual strategies overextended and applied to situations where they don’t occur.
Some illusions are simply a matter of physics.
Some illusions occur because of misleading messages from the sense organs.
Some illusions occur because the brain misinterprets sensory information.
An example of an entertaining illusion is the bent appearance of a chopstick in a half-filled glass of water.
A dangerous illusion is the more slowly moving appearance of large objects, such as trains or large trucks, that can result in serious accidents.