An undercover police officer, who had been marching with anti-police demonstrators, aims his gun at protesters after some in the crowd attacked him and his partner in Oakland, California December 10, 2014. Police said more than 100 demonstrators marched in Berkeley, California, which has a history of social activism. Under cloudy skies, turnout was smaller than earlier in the week, when demonstrators in the area threw rocks at police and shut down a major freeway. (Photo by Noah Berger/Reuters)

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

A faithful prays during the Divine Liturgy by Pope Francis at the apostolic Cathedral in Etchmiadzin, Armenia, June 26, 2016. (Photo by David Mdzinarishvili/Reuters)

Behaviour winner; Courting Royals: two royal terns in courtship display by Kristian Bell. Another beautiful morning on a beautiful beach on the Gulf Coast of Florida seemed to prompt these two royal terns to commence an intricate courtship dance. The photograph was taken with a Canon 300mm lens and 2x extender. (Photo by Kristian Bell/Deakin University/Royal Society Publishing Photography Competition 2018)

Malena, 7, looks at Belgian clown Lili Bellule at the pediatric department of the Hopital Erasme at the Universite Libre de Bruxelles (ULB), in Brussels January 27, 2015. The hospital offers performances by musicians and clowns as a form of therapy to help children cope with dealing with the stress and fear caused by hospitalization. (Photo by Yves Herman/Reuters)

People remove mud and rocks from their house after a massive landslide in Chosica, March 24, 2015. Seven people were killed and more were feared dead in Peru after a massive landslide buried parts of a town amid heavy rains, authorities said on Tuesday. Six were missing and 25 injured in the disaster in Chosica, some 30 kilometers (18.6 miles) east of Lima, said Alfredo Murgueytio, the head of the National Civil Defense Institute, Indeci. (Photo by Mariana Bazo/Reuters)

High-wire artist Kane Petersen successfully walks a tightrope 300 metres above the ground at Eureka Skydeck on September 16, 2015 in Melbourne, Australia. The walk was the highest tightrope walk ever attempted in the Southern Hemisphere. The stunt is to mark the arrival of the film “The Walk” to Australian cinemas in October. The stunt saw Kane mimic the film's French high-wire artist Philippe Petit, who successfully walked between the twin towers of the World Trade Center in 1974. (Photo by Scott Barbour/Getty Images)

Ray Yang, a celebrity trainer, takes a selfie before the start of a workout session during TV program "The Body Show" at a gym in Seoul, September 19, 2015. Looks no longer centre only on the face in beauty-obsessed South Korea, where more women are hitting the gym to improve muscle tone and physical health. As the ideal of beauty evolves in a country that is a trendsetter in cosmetics and the pursuit of plastic surgery, women's fitness has become a growth business, say purveyors of health products, from diet supplements to dumb-bells. (Photo by Kim Hong-Ji/Reuters)