The Jet Propulsion Lab team's RoboSimian robot turns on a valve at a simulated disaster-response course during day one of the Defense Advanced Research Projects Agency (DARPA) Robotics Challenge finals in Pomona, California, June 5, 2015. (Photo by David McNew/Reuters)

A firefighter battling the King Fire watches as a backfire burns along Highway 50 in Fresh Pond, California September 16, 2014. The fire led officials to call on about 400 people to evacuate from areas threatened by the blaze, Cal Fire spokeswoman Alyssa Smith said. It has charred more than 11,500 acres (4,654 hectares) and was 5 percent contained on Tuesday. (Photo by Noah Berger/Reuters)

Bangladeshi fisherman feed their otters as they catch fish in Narail some 208 kms from Dhaka on March 11, 2014. The fishermen are using a rare technique that relies on coordination between man and trained otters, a centuries-old fishing partnership that has already long died out in other parts of Asia. (Photo by Munir Uz Zaman/AFP Photo)

A woman takes a selfie next to a model of Thor during the Middle East Film & Comic Con (MEFCC) in Dubai, United Arab Emirates, Saturday, April 11, 2015. (Photo by Kamran Jebreili/AP Photo)

In this September 27, 2017 file photo, girls walk past a wall riddled with bullet holes from shootings between rival drug traffickers, at the Rocinha slum, in Rio de Janeiro, Brazil. Violence is on the rise in Rio's slums after several years of decline, and the killings of kids have shocked even residents long inured to deaths from gangs and police. (Photo by Silvia Izquierdo/AP Photo)

People wearing costumes walk during Halloween in Sierra Madre, California, U.S., October 31, 2017. (Photo by Mario Anzuoni/Reuters)

Russian cadet preparing before the International Kremlin Cadet Ball in Moscow, Russia 12 December 2017. More than 1500 students from all Russian cadets school attend in Cadet Ball. (Photo by Yuri Kochetkov/EPA/EFE)

A kite flying contest is held in Nantong, east China's Jiangsu featuring various kites of different shapes on December 20, 2017. (Photo by SIPA Asia/Pacific Press/Barcroft Images)