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)

Chinese artist Zhou Jie takes a nap on an unfinished iron wire bed, one of her sculpture works, after lunch as a friend of hers looks on at Beijing Now Art Gallery, in Beijing August 11, 2014. Zhou started her art project titled “36 Days” on August 9, in which she would live inside an exhibition hall with an unfinished iron wire bed, some iron wire sculptures in the shape of stuffed animal dolls, a certain amount of food and her mobile phone, for 36 days. The entire process is open to visitors and she may also interact with them, according to Zhou. (Photo by Jason Lee/Reuters)

Indonesian students wearing paper masks take part in the East Java Mask Parade in Surabaya, Indonesia, 13 December 2015. Thousands of people participate in the traditional parade to preserve the mask custom among the younger generation. (Photo by Fully Handoko/EPA)

Trick rider Kendel Sampson performs during the trick riding session of the RAM Rodeo in Warkworth, Ontario, on August 1, 2013. The teenage Encore Presentation Trick Riders perform daring stunts every rodeo season in towns throughout Canada. (Photo by Norm Betts/Barcroft Media)

Canada's Mandy Marchak (R) is taken down by France's Pauline Biscarat during the final match of the Hong Kong Sevens rugby women's invitational cup in Hong Kong March 28, 2014. (Photo by Tyrone Siu/Reuters)

Planes land in fog at Heathrow Airport, west London, as heavy fog covers a many parts of the south east, on April 1, 2014. (Photo by Steve Parsons/PA Wire)

A young woman dressed as a zombie takes part in a zombie parade as part of the Brussels International Fantastic Film Festival 2014 in Brussels, Belgium, 12 April 2014. More than a hundred of participants took to the streets of Brussels. (Photo by Ulien Warnand/EPA)

A tattoo of Captain America drawn by artist Sean Karon on the leg of client Ron Raucci at the Hampton Roads Tattoo Festival in Virginia, on March 2, 2012. The tattoo was completed from start to finish in one five-and-a-half hour session and won the prestigious “tattoo of the day” contest. (Photo by Jason Reed/Reuters)