Most types of humour involve the realisation of contradiction, or a mismatch, between a concept and a situation. In other words, we laugh when things surprise us because they are out of place. Even simple games like peek-a-boo have an element of surprise where someone suddenly appears out of nowhere.

Researchers think that communication is essential for humor and that humor facilitates the process of learning a language.

Imagination plays a role in incongruity. It helps children to play social roles that they usually wouldn't. Imagination begins to appear in children around 12-18 months, corresponding with the time children start to repeat parent's jokes.

Children start to produce their own jokes around two years of age, with jokes being object-based, such as putting underwear on the head. They often draw inspiration from what they are learning about. This helps them process social rules.

One of the skills that help children develop humor is knowing that people have access to different mental states and that some can have false beliefs or be deceived. When parents pretend not to see a child creeping up to scare them - this is an example of a child understanding deception.

Some research shows that this knowledge is essential for children to understand jokes involving sarcasm and irony. Children typically understand irony around five. Other researchers argue that joking develops through social interaction rather than knowledge of deception.