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)

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)

One-year-old female giant panda cub Nuan Nuan reacts inside her enclosure during joint birthday celebrations for the panda and its ten-year-old mother Liang Liang at the National Zoo in Kuala Lumpur on August 23, 2016. Giant pandas Liang Liang, aged 10, and her Malaysian-born cub Nuan Nuan, 1, were born on August 23, 2006 and August 18, 2015 respectivetly. (Photo by Mohd Rasfan/AFP Photo)

Singer Rita Ora enters her hotel on April 27, 2017 in New York City. (Photo by MEGA)

A young oriental small-clawed otter at the zoo in Neumuenster, Germany, March 5, 2014. The six young otters (one male, five female) were born on December 7, 2013. (Photo by Maja Hitij/EPA)

These are the stomach-churning pictures of the swing at the end of the world – a rickety wooden swing hanging over a precipice 2,660 metres above sea level – and not a seatbelt in sight. (Photo by Caters News)

A death mask thought to be that of English dramatist William Shakespeare (1566–1616). Found by Dr. Ludwig Becker in Mainz in 1849, the mask was linked to Shakespeare because of its 1616 date and its supposed facial resemblance to the writer. A rival theory, however, maintains that the mask is more likely to be that of English poet Ben Johnson. (Photo by Hulton Archive/Getty Images). Circa 1900

Visitors to Castle Combe take photographs in the village that was recently featured in Steven Spielberg's latest film, the wartime drama, War Horse, on January 10, 2012 near Chippenham, England. (Photo by Matt Cardy/Getty Images)