Brazil's synchronised swimmers Luisa Borges (front) and Maria Eduarda Miccuci perform during a training session at the Rio Olympic Park in Rio de Janeiro, Brazil, April 7, 2016. (Photo by Pilar Olivares/Reuters)

Festival goers kiss in the “Silent Disco” at the “Music in the Park” stage during the 50th Montreux Jazz Festival, in Montreux, Switzerland, July 9, 2016. (Photo by Anthony Anex/EPA)

Angele Blank, right, and Virginia Promeyrat wait for the start of the Greenwich Village Halloween Parade, Saturday October 31, 2015, in New York. (Photo by Tina Fineberg/AP Photo)

A visitor poses for a photograph in front of a 3D painting depicting a Japanese Imperial army soldier at a 3D art gallery in Beijing January 16, 2015. (Photo by Kim Kyung-Hoon/Reuters)

Men eat oranges from a push cart along a road as a vehicle travels past them in Karachi January 22, 2015. (Photo by Akhtar Soomro/Reuters)

Arctic wolves in their new enclosure in the wildlife park in Hanau, Germany, 10 February 2015. The pack is one of the park's main attractions, which specializes in local and European breeds. (Photo by Boris Roessler/EPA)

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)

Opossums on their mothers back at a game reserve in Central Minnesota, USA, on September 2, 2013. (Photo by Caters News Agency)