Police officers escort people from inside the shopping center as they respond to a shooting at the Olympia Einkaufzentrum (OEZ) at July 22, 2016 in Munich, Germany. According to reports, several people have been killed and an unknown number injured in a shooting at a shopping centre in the north-western Moosach district in Munich. Police are hunting the attacker or attackers who are thought to be still at large. (Photo by Joerg Koch/Getty Images)

Thailand's Puttita Supajirakul is down on the court after a point during a women's doubles badminton match against the Netherlands at the 2016 Summer Olympics in Rio de Janeiro, Brazil, August 11, 2016. (Photo by Kin Cheung/AP Photo)

A workman walks past a large mural on the side of a building during the “Sand Sea & Spray” Urban Art Festival in Blackpool, north west England on July 11, 2015. (Photo by Oli Scarff/AFP Photo)

Soldiers of China's People's Liberation Army (PLA) jump as part of their winter training in temperature of negative 26 degrees Celsius at China's border with Russia in Heihe, Heilongjiang province, December 14, 2015. (Photo by Reuters/Stringer)

Aldi SugandaRizal (2 years-old) smoking a cigarette while playing at the family home in Sekayu district, South Sumatera, Indonesia on May 23, 2010. (Photo by Ardiles Rante/Barcroft Media)

The US Navy Blue Angels numbers 5 and 6 fly below Sean Tucker (above) as he pilots the Oracle Challenger III over San Francisco, California as part of a practice run for Fleet Week on October 6, 2016. (Photo by Josh Edelson/AFP Photo)

Members of the Iraqi Army fire towards Islamic State militant positions at the south of Mosul, Iraq December 10, 2016. (Photo by Alaa Al-Marjani/Reuters)

Brain-on-a-chip. Dazzling in green and magenta this image shows the nerve fibres (in green) produced by neural stem cells (in magenta) as they grow on a synthetic gel. Captured by a technique known as confocal microscopy, the image is part of research shedding light on how tinkering with the environment can affect the way in which nerve fibres grow. (Photo by Collin Edington and Iris Lee/Massachusetts Institute of Technology/Wellcome Images)