Attempts to define laughter/amusement (as one of the six or seven basic emotional responses: anger, sadness, happiness, fear, disgust…) tend to focus on the fact that it usually requires some aspect of surprise.  Both babies and juvenile chimpanzees laugh at 'peekaboo' games because they lack a sense of object…

Pff.  Any fool knows that Halloween is the sexiest holiday: it's when women all agree to dress like slutty cats, slutty witches, etc.