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We examine the behavior of call options surrounding the underlying stock's ex-dividend date. The evidence is inconsistent with the predictions of a rational exercise policy; a significant fraction of the open interest remains unexercised, resulting in a windfall gain to option writers. This triggers a sophisticated trading scheme that enables short-term traders to receive a significant fraction of the gains. The trading scheme inflates reported volume and distorts its traditional relations to liquidity. The dramatic increases in the volume of trade on the last cum-dividend day are facilitated by limitations on transaction costs passed by the various option exchanges. The Author 2009. Published by Oxford University Press on behalf of The Society for Financial Studies. All rights reserved. For Permissions, please e-mail: [email protected]., Oxford University Press.