Humour or humor (see spelling differences) is the tendency of particular cognitive experiences to provoke laughter and provide amusement. Many theories exist about what humour is and what social function it serves. People of all ages and cultures respond to humour. The majority of people are able to be amused, to laugh or smile at something funny and thus they are considered to have a "sense of humour". The term derives from the humoral medicine of the ancient Greeks, which stated that a mix of fluids known as humours (Greek: χυμÏŒς, chymos, literally juice or sap, metaphorically, flavour) controlled human health and emotion. A sense of humour is the ability to experience humour, although the extent to which an individual will find something humorous depends on a host of variables, including geographical location, culture, maturity, level of education, intelligence and context. For example, young children may favour slapstick, such as Punch and Judy puppet shows or cartoons such as Tom and Jerry. Satire may rely more on understanding the target of the humour and thus tends to appeal to more mature audiences. Nonsatirical humour can be specifically termed "recreational drollery". Alastair Clarke explains: "The theory is an evolutionary and cognitive explanation of how and why any individual finds anything funny. Effectively, it explains that humour occurs when the brain recognizes a pattern that surprises it, and that recognition of this sort is rewarded with the experience of the humorous response, an element of which is broadcast as laughter." The theory further identifies the importance of pattern recognition in human evolution: "An ability to recognize patterns instantly and unconsciously has proved a fundamental weapon in the cognitive arsenal of human beings. The humorous reward has encouraged the development of such faculties, leading to the unique perceptual and intellectual abilities of our species."