An inhalation and an exhalation; a cadenza of comprehension; a suspension and a resolution; a momentary off-balance followed by a return to balance; a moment of discovery or recognition; a flash of insight; a movement to a new understanding; a change in consciousness; an expression of the character's inner action. Something that you can let happen, but not make happen. An important tool for both analysing a character's subtext, and making comedy work. Comedy is many little ah-ha's. Tragedy is one long sustained ah-ha.
According to Professor John Kounios of Drexel University, his studies into brain science have demonstrated that there is a distinct neurological difference between arriving at a discovery through insight or through analysis.