Hidden messages can drive you to drink. Psychologists sat 39 volunteers in front of computers displaying faces with neutral expressions on them. Unbeknownst to subjects, the computers subliminally flashed smiling or angry faces for 1/25 of a second for every second of neutral expression. When given cups of lemon-lime drink, volunteers who said they were thirsty before the experiment drank more than double after happy faces than after frowns. In a variation of the experiment, highly thirsty participants exposed to hidden smiles were willing to pay up to triple the price for the drink than others shown grimaces. No volunteers reported consciously seeing the subliminal faces. Being thirsty beforehand was key; subjects who were not apparently remained unaffected. Piotr Winkielman of the University of California at San Diego and his colleagues presented their findings on May 28 at the American Psychological Society meeting in Los Angeles.