Unexpected.

Caravaggio, Judith and Holofernes (detail), 1599

Strangeness is the indispensable condiment of all beauty.That which is not slightly distorted lacks sensible appeal; from which it follows that irregularity – that is to say, the unexpected, surprise and astonishment, are a essential part and characteristic of beauty. The study of beauty is a duel in which the artist cries with terror before being defeated.

Charles Baudelaire