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Embryoids like this one are created from stem cells and resemble very primitive human embryos. Scientists are studying them in hopes of learning more about basic human biology and development. Courtesy of Rockefeller University hide caption

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Courtesy of Rockefeller University

This synthetic stingray is made of gold, silicone and live muscle cells from a rat. Scientists use pulses of light to guide its propulsion. Karaghen Hudson and Michael Rosnach/Science hide caption

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Karaghen Hudson and Michael Rosnach/Science

Synthetic Stingray May Lead To A Better Artificial Heart

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A Fitbit Saved His Life? Well, Maybe

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Ben Lecomte has swum across the Atlantic Ocean, and now he aims to traverse the Pacific, which will take him five or six months. Bongani Mlambo/The Longest Swim hide caption

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Bongani Mlambo/The Longest Swim

Can Extreme Exercise Hurt Your Heart? Swim The Pacific To Find Out

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Twitter changed its "favorite" star icon to a "like" heart icon prompting largely negative responses from Twitter users. But is it the heart they hate? Or the change itself? Screenshot by NPR hide caption

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Screenshot by NPR

In addition to heart problems triggered by some supplements, emergencies often arise when kids swallow dietary supplements meant for adults, according to the CDC analysis, or when older adults choke on the pills. Lee Woodgate/Ikon Images/Corbis hide caption

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Lee Woodgate/Ikon Images/Corbis

Dietary Supplements Send Thousands To ERs Yearly

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Meredith Rizzo/NPR

A Metronome Can Help Set The CPR Beat

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Members of the Mormon Tabernacle Choir raise their voices in unison — and perhaps unify their heart rates, too. George Frey/Getty Images hide caption

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George Frey/Getty Images