Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)

A Sikh warrior, wearing a huge turban attends the annual fair of “Hola Mohalla” in Anandpur Sahib, in the northern Indian state of Punjab, Monday, March 17, 2014. Believers from various parts of northern India collect at the religious fair to celebrate the festival of Holi in a tradition set by the tenth Sikh guru Guru Gobind Singh in the seventeenth century. Nihangs, or Sikh warriors, display their martial skills and attire during the fair, believed to be maintained in the exact tradition as set by the Guru. (Photo by Altaf Qadri/AP Photo)

A costumed fan attends Comic-Con International 2014 – Day 1 on July 24, 2014 in San Diego, Calif. (Photo by Joe Scarnici/FilmMagic/Getty Images)

A sun bear is offered chocolate by a visitor in its enclosure at a zoo in Bandung on January 18, 2017. Animal rights activists on January 18 demanded the closure of an Indonesian zoo after skeletal sun bears were pictured begging for food from visitors and eating their own dung. (Photo by Timur Matahari/AFP Photo)

Participants lay down on a street covered by coloured powder during the annual Bangkok Color Run in Bangkok, Thailand April 1, 2017. (Photo by Athit Perawongmetha/Reuters)

Passengers wear no trousers as they ride the London Underground in London, Britain, 07 January 2018. The No Pants Subway Ride is an global annual event where people take the public transport while they are not wearing trousers to surprise other passengers. This event takes place on the first Sunday of every year in the world's major cities. (Photo by Tolga Akmen/EPA/EFE/Rex Features/Shutterstock)

Gold medalists Kikkan Randall and Jessica Diggins of the United States dancing during the medal ceremony for Cross-Country Skiing – Ladies' Team Sprint Free on day 13 of the PyeongChang 2018 Winter Olympic Games at Medal Plaza on February 22, 2018 in Pyeongchang-gun, South Korea. (Photo by Eric Gaillard/Reuters)