An image believed to be that of a hole-punch cloud. Scientists say airplanes create these patterns when they fly through certain types of clouds. The water in the clouds can turn to rain or snow and fall to the ground. H. Raab/Vesta/Wikimedia Commons hide caption

itoggle caption H. Raab/Vesta/Wikimedia Commons

Mighty Mouse? Male Alston's mice use high-frequency songs to entice females. Bret Pasch/University of Florida hide caption

itoggle caption Bret Pasch/University of Florida

This image from April 27 shows a series of tornadoes forming over Alabama and Mississippi. Captured from a satellite orbiting located at a fixed location above Earth, images like these help track trends in weather patterns. Another set of polar-orbiting satellites are useful for long-term forecast predictions. NASA Earth Observatory hide caption

itoggle caption NASA Earth Observatory

By juicing up special cardiac stem cells, researchers hope to find a way for human hearts to heal when they're injured by a heart attack. PRNewsFoto/Zygote Media Group, Inc. via AP hide caption

itoggle caption PRNewsFoto/Zygote Media Group, Inc. via AP

Scientists have known for a long time that nicotine decreases appetite among smokers, but they didn't know why. A new study finds that nicotine triggers a response in certain specific brain cells known to regulate appetite. iStockphoto.com hide caption

itoggle caption iStockphoto.com

A female mosquito acquires a blood meal. This species, Aedes aegypti, carries and transmits the dengue fever virus. James Gathany/CDC hide caption

itoggle caption James Gathany/CDC

NASA engineer Ernie Wright looks on as the first six primary mirror segments for the James Webb Space Telescope are prepped to begin final cryogenic testing at NASA's Marshall Space Flight Center. The telescope will have 18 primary mirror segments. David Higginbotham/NASA hide caption

itoggle caption David Higginbotham/NASA