Iraqi forces gather during an operation to attack Islamic State militants in Mosul, Iraq, October 21, 2016. (Photo by Reuters/Stringer)

A runner in fancy dress participates in the Virgin London Marathon 2013 on April 21, 2013 in London, England. (Photo by Tom Dulat/Getty Images)

A Saudi soldier fires a mortar towards Houthi movement position, at the Saudi border with Yemen April 21, 2015. (Photo by Reuters/Stringer)

A participant races in the Brompton World Championship in Bern, Switzerland October 21, 2018. (Photo by Stefan Wermuth/Reuters)

Birds sit on the back of a zebra in the Nairobi National Park, near Nairobi, Kenya, November 21, 2018. (Photo by Baz Ratner/Reuters)

Dancers perform “El torito”, during a celebration honoring Saint Thomas, the patron saint of Chichicastenango, Guatemala, Saturday, December 21, 2019. The Feast of Saint Thomas draws international tourists with its colorful pageantry, but at its heart is a religious celebration melding Catholic and indigenous traditions that culminates on Dec. 21. (Photo by Moises Castillo/AP Photo)

A Spanish recortador jumps over a bull during a show in Cali December 21, 2014. (Photo by Jaime Saldarriaga/Reuters)

A “Free Syrian Army” fighter in the Bustan Pasha neighborhood of Aleppo, Syria, August 21, 2013. (Photo by James Lawler Duggan)