The word humour comes from the Greek humoral referring to medicine (humours) that was thought to control human health and emotion whereas a sense of humour is the ability to experience humour. Humour depends on culture, education, intelligence and also context. Humour also has many variations such as slapstick thought to be a rudimentary form, and satire which was thought to be a more educated version. Laughter, on the other hand, is what results from humour and helps clarify emotional context (by defining amusement) between people.

Humour is deeply rooted in human evolution and is thought to be centered in two regions of the brain containing von Economo neurons which help us move though a complex social environment. Since laughter is universal it is thought to be a tool used to break down boundaries between people and cultures and create bonds. Laughter, as we shall see, is contagious and releases a host of pleasurable hormones throughout the body. An entire branch of therapy exists devoted to laughter as medicine.

In this chapter we will examine the different types of smiles including the Duchenne smile, the tight lipped smile (high and low intensity), uneven smile, the upper smile, the grin or smirk and the broad smile. We also cover the origination of smiles and laughter, their contagion, how they generate leniency and who smiles more, men or women. We will also hit on laughing cycles, the theory of jokes and when to avoid telling dirty jokes, why women should not grunt when they laugh and how laughter is linked to health.