Fighters of the Popular Resistance Committees stand during a graduation ceremony of the affiliate special forces of the Popular Resistance, in Yemen's southwestern city of Taiz October 8, 2015. (Photo by Reuters/Stringer)

The Jet Propulsion Lab team's RoboSimian robot turns on a valve at a simulated disaster-response course during day one of the Defense Advanced Research Projects Agency (DARPA) Robotics Challenge finals in Pomona, California, June 5, 2015. (Photo by David McNew/Reuters)

Cambridge students the morning after the Trinity and Jesus college May Balls in Cambridge, United Kingdom on June 19, 2018. Students at Cambridge University celebrate the end of the academic year with the May Balls. (Photo by South West News Service)

Iranian soccer fan wait for the start of the group B match between Iran and Spain at the 2018 soccer World Cup in the Kazan Arena in Kazan, Russia, Wednesday, June 20, 2018. (Photo by Diego Azubel/EPA/EFE)

Adolf Hitler (left), German Nazi politician, in a deck chair next to is niece Angela (Geli) Raubal – around 1930. (Photo by Ullstein Bild/Ullstein Bild via Getty Images)

In this November 2, 2018 photo, a voodoo believer who is supposed to be possessed with Gede spirit performs rituals near Baron Samedi's tomb during the annual Voodoo festival Fete Gede at Cite Soleil Cemetery in Port-au-Prince, Haiti. As a proof that they got into trance and their bodies got possessed by Gedes, they drink and wash their faces, their eyes and even their genitals with a mixture of raw rum and hot chili peppers that, according to believers, could burn the skin of any human alive. (Photo by Dieu Nalio Chery/AP Photo)

Princess Diana relaxes on the sand during a visit to the beach on the Caribbean Island of Nevis January 4, 1993. (Photo by Mark Cardwell/Reuters)

In this photo taken on Sunday, January 14, 2018, Anastasia Gruzdeva, left, poses for selfie with her friends as the temperature dropped to about –50 degrees (–58 degrees Fahrenheit) in Yakutsk, Russia. Temperatures in the remote, diamond-rich Russian region of Yakutia have dropped to near-record lows, plunging to –67 degrees Centigrade (-88.6 degrees Fahrenheit) in some areas. (Photo by Sakhalife.ru Photo via AP Photo)