“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)

(L-R) Senior Drum Major Betts of the Scotts Guard, Bugler Lee Kidd, Guardsman Adam Deer of the Coldstream Guards and Lance corporal Michael Strong of the Princess of Wales's Royal Regiment pose in their full ceremonial attire at Wellington Barracks on March 21, 2012 in London, England. The group make up part of the ceremonial military personnel who will play a key role during Her Majesty the Queens Diamond Jubilee celebrations between June 2–5. (Photo by Dan Kitwood/Getty Images)

Armed Yemeni children sit in the back of a pick up truck with fighters loyal to Yemen's Saudi-backed President Abedrabbo Mansour Hadi in the Dar saad neighbourhood of the southern Yemeni city of Aden on May 10, 2015, as they continue to battle Shiite Huthi rebels. (Photo by Saleh Al-Obeidi/AFP Photo)

A former paratrooper demonstrates his strength and skills while lifting a chair during the celebrations for the Paratroopers Day at the Central park in the Siberian city of Krasnoyarsk, Russia, August 2, 2015. Paratroopers are an elite unit of the Soviet Army, and everyone in the country recognize their blue berets. (Photo by Ilya Naymushin/Reuters)

North Koreans who signed up to join the army train in the midst of political tension with South Korea, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang August 23, 2015. Top aides to the leaders of North and South Korea resumed talks on Sunday after negotiating through the night in a bid to ease tensions involving an exchange of artillery fire that brought the peninsula to the brink of armed conflict. (Photo by Reuters/KCNA)

People look at revellers (L) waiting to take part in a LGBT (lesbian, gay, bisexual and transgender) pride parade to mark Gaijatra Festival, also known as the festival of cows, in Kathmandu, Nepal, August 30, 2015. Hundreds of lesbians, gays, bisexuals and transvestites paraded through Nepal's capital Sunday to demand that rights for sexual minorities be included in the country's new constitution that is being finalized. (Photo by Navesh Chitrakar/Reuters)

A tearful Beatle lover pleads unsuccessfully with a policeman to carry her fan button to Ringo, one of the four mop-top singers who drew squeals and shrieks from more than 30,000 spectators at two Indiana State Fair shows in Indianapolis on September 4, 1964. (Photo by Bob Daugherty/AP Photo)

The jewelled flower mantis, commonly found in Asia, is believed to be the inspiration for many martial artists is seen in Jakarta, Indonesia on August 2, 2016. (Photo by Prabu Dennaga/Barcroft Images)