In Othello (Act 3, scene 3, 165–171), Shakespeare turned jealousy into a true beast. He is comparing jealousy (the 'green-ey'd monster') to a cat, as many cats have green eyes. And, before the cat kills his prey, he tortures it ('which doth mock').

The notion that jealousy is green-eyed is probably older than Shakespeare, although Shakespeare is one of the earliest authority in print. In The Merchant of Venice, Portia refers to "green-eyed jealousy" (Act 3, scene 2). In Othello, Shakespeare coins the more intense phrase "green-ey'd monster." Renaissance Englishmen often paired colors with emotions or personal qualities. Both green and yellow were emblematic of jealousy, and green is also emblematic of envy. Some colors were associated with the bodily fluids or laughter. They were thought to make up a person's temperament. Green and black were the colors attributed to bile.

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