Researchers at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., use eggs to see if the Asian strain of the H5N1 bird flu virus has entered the U.S. in this photo from 2006. Andy Manis/AP hide caption

itoggle caption Andy Manis/AP

Researchers in Australia found that when they removed mistletoe from large sections of forests, vast numbers of birds left. BSIP/UIG via Getty Images hide caption

itoggle caption BSIP/UIG via Getty Images

Brain scans using Amyvid dye to highlight beta-amyloid plaques in the brain. Clockwise from top left: a cognitively normal subject; an amyloid-positive patient with Alzheimer's disease; a patient with mild cognitive impairment who progressed to dementia during a study; and a patient with mild cognitive impairment. Slide courtesy of the journal Neurology hide caption

itoggle caption Slide courtesy of the journal Neurology

A section of the Sutter's Mill meteorite, dubbed "Darth Vader," is studied at a lab at the University of California, Davis. The meteorite is made of carbonaceous chondrite, which contains materials that formed the planets of the solar system. UC Davis hide caption

itoggle caption UC Davis

Bali sea salt and a spoonful of Hawaiian red alae salt. Jim Noelker/AP hide caption

itoggle caption Jim Noelker/AP

Chimpanzees check out a termite mound at the Chimp Haven sanctuary in Louisiana. Chimp Haven hide caption

itoggle caption Chimp Haven

For centuries, Russians believed putting a brown frog in their milk would keep it fresh. Now scientists are finding chemicals in the frog's slimy goo that inhibit the growth of bacteria and fungi. Stefan Arendt/Corbis hide caption

itoggle caption Stefan Arendt/Corbis