Squirrels closely mimic bird warning calls and help spread the alarm through the forest that hawks, owls or other predators are nearby. iStockphoto hide caption

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An impala strikes a pose under a forest canopy in Zimbabwe. Morkel Erasmus/Getty Images/Gallo Images hide caption

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Frozen tuna lies on the ground at the Tsukiji fish market in Tokyo. The FDA recommends freezing raw fish before serving it in sushi as a way to keep it free of parasites. But as a recent outbreak of Salmonella in the U.S. highlights, freezing doesn't guarantee that raw sushi fish is pathogen-free. Koichi Kamoshida/Getty Images hide caption

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The uptick in serious bike injuries occurred for both male and female cyclists, although more men get in accidents each year. Justin Sullivan/Getty Images hide caption

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Yellowtail jack (Seriola lalandi) at HSWRI in San Diego. Courtesy of HSWRI hide caption

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Copenhagen, Denmark - October 11, 2014: fruits and vegetables stalls at market in Copenhagen. Customers are choosing goods for themselves. These stalls is located between market halls where one can find over 60 stands with everything from fresh fish and meat, as well as small places to get a quick bite. It is located near Nørreport metro station. iStockphoto hide caption

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People who don't get enough sleep show higher levels of inflammation, say scientists who study colds. Smoking, chronic stress and lack of exercise can make you more susceptible to the viruses, too. Frederic Cirou/PhotoAlto/Corbis hide caption

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"Probably females are better at accessing olfactory memories, but I don't know why," says Robert Bath, a wine and beverage studies professor at the Culinary Institute of America in Napa Valley. "Maybe men don't pay as much attention?" Maria Fabrizio for NPR hide caption

itoggle caption Maria Fabrizio for NPR