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)

Newlyweds take wedding photos hanging from bridge, Yueyang, Hunan province, China on August 9, 2016. They held such a special wedding ceremony on China's Qixi Festival. (Photo by Top Photo Corporation/Rex Features/Shutterstock)

A greater bird of paradise (Paradisaea apoda) displaying in Badigaki Forest, Wokam Island (Aru Islands, Indonesia). Found here in Aru and on adjacent New Guinea, the greater bird of paradise represents about 40 different species of birds of paradise that depend on intact rainforest across the New Guinea region spanning eastern Indonesia and Papua New Guinea. With more than 80% of forest cover still intact, this region represents the largest remaining block of rainforest in the entire Asia-Pacific. (Photo by Tim Laman/naturepl.com/LDY Agency)

Enya Kim from the Natural History department at auctioneers Bonhams & Butterfields stands in front of one of the world's largest set of shark jaws comprised of about 180 fossil teeth from the prehistoric species, Carcharocles megalodon, which grew to the size of a school bus, at the Venetian Resort Hotel Casino September 30, 2009 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)

Visitors look at a giant puppet of a grandmother sleeping on a bed inside St George's Hall in Liverpool, northern England July 23, 2014. The grandmother is one of two giant models made for a World War I commemorative event. (Photo by Nigel Roddis/Reuters)

The two Pulis Quastie and Gin-Gin run in the snow in their garden in Lautertal, southern Germany, Thursday, January 5, 2017. (Photo by Michael Probst/AP Photo)

People stand around a leopard with its head stuck in a vessel in Rajsamand district of Rajasthan state, India, Wednesday, September 30, 2015. The leopard's head got stuck when it attempted to drink water from the pot, according to news reports. Forest officials tranquilized the animal and sawed off the vessel later in the day. (Photo by Kabir Jethi/AP Photo)

Spectators dressed as leprechauns attend St Patrick's Day parade in Dublin on March 17, 2014. (Photo by Peter Muhly/AFP Photo)