Metallica and Lang Lang rehearse for THE 56TH ANNUAL GRAMMY AWARDS music industry's premier event takes place Sunday, Jan. 26 (8:00-11:30 PM, live ET/delayed PT) at STAPLES Center in Los Angeles on the CBS Television Network. Photo: Heather Wines/CBS ©2014 CBS Broadcasting, Inc. All Rights Reserved

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)

A giant river otter, the world's largest otter species, looks out of its enclosure at the newly completed River Safari in Singapore, on March 25, 2013. (Photo by Wong Maye-E/Associated Press)

An incredible view of daytime lightning on Saturn during one of the biggest storms the ringed planet has ever seen has been captured by a NASA spacecraft.

Photo: The huge storm which generated the lightning strike on Saturn can be seen in the top right of this image. (Photo by NASA)

A woman is detained by security forces after looting broke out during an ongoing blackout in Caracas, Venezuela, March 10, 2019. (Photo by Ivan Alvarado/Reuters)

A competitor shouts as he takes part in the “Tough Guy” adventure race near Wolverhampton, central England, on January 29, 2017. The Tough Guy event, which is being held for the final time in its 30th year, challenges thousands of competitors to run a gruelling course whilst negotiating over 200 obstacles including: water, fire, and tunnels. (Photo by Oli Scarff/AFP Photo)

A man holds on a rope as he tries to board a truck while crossing floodwaters brought by typhoon Koppu that battered Candaba town, Pampanga province, north of Manila October 20, 2015. Typhoon Koppu swept across the northern Philippines killing at least nine people as trees, power lines and walls were toppled and flood waters spread far from riverbeds, but tens of thousands of people were evacuated in time. (Photo by Romeo Ranoco/Reuters)

This artist image released from Japan's airline All Nippon Airways (ANA) on April 17, 2015 shows ANA's Boeing 787-9 aircraft into the colors of R2-D2 robot of Star Wars. Japanese air carrier ANA will place the special colored jetliner in service in this autumn. (Photo by AFP Photo/All Nippon Airways)