A competitor poses on the catwalk during the Miss Bumbum Brazil 2016 pageant in Sao Paulo, Brazil on November 9, 2016. Fifteen candidates compete in the annual pageant to select Brazil' s sexiest female rear end. (Photo by Miguel Schincariol/AFP Photo)

A man presents a self-made robot that local media reported is able to carry a person, in Heihe, Heilongjiang province, China, April 5, 2017. (Photo by Reuters/China Daily)

A woman smokes marijuana during the annual 4/20 marijuana rally on Parliament Hill in Ottawa, Ontario, Canada, April 20, 2017. (Photo by Chris Wattie/Reuters)

Muslim children play sack race during Eid-al-Fitr celebration in Taguig city, south of Manila July 18, 2015. (Photo by Romeo Ranoco/Reuters)

Pakistani laborers transport the front portion of a vehicle using a handcart at a road in Peshawar, Pakistan, Monday, August 3, 2015. (Photo by Mohammad Sajjad/AP Photo)

A glasses-free Toshiba 55-inch 3-D 4x full HD TV shows the movie, “Coraline” at the 2012 International Consumer Electronics Show at the Las Vegas Convention Center January 11, 2012 in Las Vegas, Nevada. The TVs are scheduled to be available this year and will come with embedded cameras with facial recognition capability so depending on where you are sitting, the set will adjust the viewing point for the best 3-D experience. (Photo by Ethan Miller/Getty Images)

A Pakistani child, whose family was displaced by 2010 floods from a village in Pakistan's Sindh province, sits on a wooden cart outside her family's makeshift home, in a slum on the outskirts of Islamabad, on February 8, 2013. (Photo by Muhammed Muheisen/AP Photo)

“Hippo Chase”. As we approached the camp the Selinda Reserve of northern Botswana our boat passed by a hippo resting in the water. I turned around to look back at the boat's wake and saw the hippo charging after us! The hippo must've been tired from an all-nighter because he was angry. He rose way up out of the water three times trying to chase our boat! He was coming at us with such force that he created a wake of his own. Photo location: Selinda Reserve of northern Botswana. (Photo and caption by Curtis Simmons/National Geographic Photo Contest)