Only sane brains have sane sense of humour, which is connected to the logic center and allows to understand the difference between normality and abnormality, ergo wisdom and absurdity. Normal people are able to use the sense of humour to create tasteful irony, comedy and satire in order to evidence and reflect on anything. Abnormal people with degenerated brains don't have it at all, or have gross and spiteful sense of humour that is defined as sick and demented.