A performer dances at a housing exhibition in Wuhan, Hubei province, China, September 27, 2015. (Photo by Reuters/Stringer)

A man washes his horse as a woman bathes her son at concrete water pens under a flyover in a slum area in Kolkata, India October 21, 2016. (Photo by Rupak De Chowdhuri/Reuters)

Wadha al-Sayyed, wife of captive Lebanese soldier Khaled Moqbel, protests for his release and government action, near burning tyres blocking a road in Beirut, December 15, 2014. More than two dozen members of the Lebanese security forces are being held by Sunni Islamists. (Photo by Hasan Shaaban/Reuters)

South Korean rescue members wearing chemical protective suits walk past a monster character (R) during an anti-terror drill as part of a disaster management exercise at the COEX shopping and exhibition center in Seoul on May 20, 2016. South Korea is holding its 2016 Safe Korea anti-disaster exercise this week against terrorist threats and natural disasters. (Photo by Jung Yeon-Je/AFP Photo)

Aiden Haas, left, and Lilli Alcala pose after being crowned Mud King and Mud Queen at the 29th annual Mud Day, Tuesday, July 12, 2016 in Westland, Mich. The event, open to children 12 and younger, was at the Hines Park-Nankin Mills Area west of Detroit. Children 12 and younger were able to slosh around in the pit while participating in mud limbo, wheelbarrow races and other free activities. (Photo by Carlos Osorio/AP Photo)

Auditioning performers follow resident choreographer Erik Sorensen, center back, at the Sydney Dance Company in a routine during castings in Moulin Rouge's current show “Féerie”, in Sydney, Australia, Thursday, July 28, 2016. The show's artistic team is in Australia to choose new talent to perform with one of the most famous cabarets that has been illuminating Paris since 1889. (Photo by Rob Griffith/AP Photo)

A reveler, dressed as a Brazilian national army soldier holding a mock weapon with flowers jutting out of it, participates in the annual Gay Pride Parade in Sao Paulo, Brazil, Sunday, June 18, 2017. (Photo by Nelson Antoine/AP Photo)

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)