A zookeeper feeds a hippopotamus with a watermelon in its enclosure in Belgrade's zoo, Serbia, July 20, 2015. Temperatures in Serbia have risen up to 40 degrees Celsius (104 degrees Fahrenheit), according to official meteorological data. (Photo by Marko Djurica/Reuters)

Keira Knightley attends the premiere for “A Dangerous Method” at The 55th BFI London Film Festival at The Odeon West End on October 24, 2011 in London, United Kingdom. (Photo by Dave Hogan/Getty Images)

Two Bunny Girls from the Playboy Club and two Penthouse Pets from the Penthouse Club prepare to take part in the annual Good Friday waiters and waitresses race in Battersea Festival Gardens, London, 28th March 1972. (Photo by Ian Showell/Keystone/Hulton Archive/Getty Images)

Apple CEO Tim Cook discusses the new iPhone 6 and iPhone 6 plus on Tuesday, September 9, 2014, in Cupertino, Calif. The iPhone 6 will have a screen measuring 4.7 inches, while the iPhone 6 Plus will be 5.5 inches. (Photo by Marcio Jose Sanchez/AP Photo)

Flash, a golden retriever, plays with a toy following a press event for the American Kennel Club to reveal the nations most popular dog breeds in the Manhattan borough of New York, February 22, 2016. (Photo by Carlo Allegri/Reuters)

Chinese woman Zhang Jing, known as the “Ugly Girl” smiles after doctors removed the stitches from her fourth session of cosmetic surgery at a hospital on March 23, 2005 in Shanghai, China. Zhang Jing, 26 years old, from Tianjin Municipality, was forced to leave school because her classmates sneered at her appearance during her teenage years. After leaving junior high school, Zhang found herself still unacceptable by society, she struggled to look for a job, but was turned down by one thousand job applications in ten years. Zhang's story was widely reported by the media in 2003, this helped her find a job and get three chances of free plastic surgery. (Photo by China Photos/Getty Images)

Members of Japan's idol group “Virtual Currency Girls” wearing cryptocurrency-themed masks perform in their debut stage in Tokyo, Japan, January 12, 2018. Japanese female idols have teamed up to form the ‘Virtual Currency Girls’ group to promote the knowledge of cryptocurrencies through entertainment. Each of its 8 members represents a cryptocurrency: bitcoin cash, bitcoin, ether, neo, nem, ripple, mona, and cardano. (Photo by Kim Kyung-Hoon/Reuters)