Can You Help Me Tie My Shoe? Researchers found that when study participants were asked an unusual request, they were more likely later on to perform a favor. iStockphoto.com hide caption

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At the International AIDS conference, a female condom fashion show raised awareness about the rising need for more female condoms. Olwin Manyanye of Zimbabwe shows off one of the dresses decorated with a second-generation female condom, called "FC2." Benjamin Morris/NPR hide caption

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Researchers studying brains want to know what's happening in an area called the premotor cortex — the place in the brain that gears up for something the body is about to do, like swimming. Above, Michael Phelps dives off the starting blocks in the final heat of the men's 400-meter individual medley during the 2012 U.S. Olympic Swimming Team Trials in Omaha, Neb., on June 25. Jamie Squire/Getty Images hide caption

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A 3-D model of HIV peeled back to show its layers. HIV's genetic material sits inside a spherical shell (gray matrix) studded with spikes (dark gray and orange). The sphere pops open when a T cell tugs on a spike. Courtesy of Ivan Konstantinov/© Visual Science 2011 hide caption

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A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/via Wikimedia Commons hide caption

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Texas Gov. Rick Perry is the latest state executive to say no to an expansion of Medicaid. Win McNamee/Getty Images hide caption

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Kailash Sundaran (left), Devyn Greenberg and Devontae Freeland celebrate the Supreme Court's ruling upholding the Affordable Health Care Act outside the court Thursday. Alex Wong/Getty Images hide caption

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San Juan Creek meets the Pacific Ocean at Doheny State Beach in Dana Point, Calif. The poor water quality off Doheny State Beach put in a list of worst beaches in the U.S. Reed Saxon/AP hide caption

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