Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)

A frog sits on a leaf and instead of seeing a reflection of itself in the water below, it sees a snail, attached to the bottom of the leaf, in a fish tank in Vietnam. (Photo by Duong Quoc Dinh/Solent Ne/SIPA Press)

A bear that wandered into a University of Colorado Boulder dorm complex falls from a tree after being tranquilized by Colorado wildlife officials on April 26, 2012. Colorado wildlife official Jennifer Churchill said that the 200-pound male bear was tagged and relocated to a remote Rocky Mountain area. The bear was hit by two cars on May 3 and died. (Photo by Andy Duann)

British comedian and director Charles Chaplin (1889–1977) and actress Paulette Goddard (1911–1990), to whom he was married for seven years, star in the comedy “Modern Times”, directed by Chaplin himself. (Photo by Hulton Archive/Getty Images). 1936

Yanelis Blanco, 24, center, dances with a group of friends at Santa Maria beach, about 15 miles from Havana. It is the closest beach to Havana. Others, from left to right are Jackson Miranda, 21, Dayan Suarez, 24, and Melisa Oliva, 15. The men in the group have a rap group together. The government is demolishing buildings all over the coast of East Havana and recovering and restoring beach dunes. (Photo by Sarah L. Voisin/The Washington Post)

Prince Charles, Prince of Wales (R) and Camilla, Duchess of Cornwall (L) visit Seppeltsfield Winery in Barossa Valley, Australia, 10 November 2015. The royal couple are on a 12-day tour visiting seven regions in New Zealand and three states and one territory in Australia. (Photo by Daniel Kalisz/EPA)

People stand around a leopard with its head stuck in a vessel in Rajsamand district of Rajasthan state, India, Wednesday, September 30, 2015. The leopard's head got stuck when it attempted to drink water from the pot, according to news reports. Forest officials tranquilized the animal and sawed off the vessel later in the day. (Photo by Kabir Jethi/AP Photo)

Peruvian shamans holding a poster of Russia's President Vladimir Putin perform a ritual of predictions for the new year at Morro Solar hill in Chorrillos, Lima, Peru, December 29, 2015. The ritual is an end-of-the-year tradition and the shamans called for world peace and wished good luck for the upcoming elections in Peru and the U.S. (Photo by Mariana Bazo/Reuters)