A turkey vulture makes quick work of a dead rabbit at Martin Luther King Jr. Regional Shoreline park in Oakland, Calif. Sebastian Kennerknecht/Minden/Corbis hide caption

itoggle caption Sebastian Kennerknecht/Minden/Corbis

A tangle of protein (green) in this scanning electron micrograph of a brain cell of an Alzheimer's patient lies within the cytoplasm (blue) of the cell. The tangle consists of clumps of a toxic form of tau. Thomas J. Deerinck/Corbis hide caption

itoggle caption Thomas J. Deerinck/Corbis

A nurse adjusts the position of a patient's arm during dialysis treatment. The treatment requires trained staff that weren't readily available in the aftermath of Hurricane Sandy. Michael Donne/Science Source hide caption

itoggle caption Michael Donne/Science Source

This is a re-creation of a color plate from Interaction of Color, by Josef Albers. The two X's are are exactly the same — it's the different backgrounds that make them look like very different colors. Source: Josef Albers Interaction of Color hide caption

itoggle caption Source: Josef Albers Interaction of Color