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 model is filmed backstage before the Jeremy Scott Fall/Winter 2015 collection presentation at New York Fashion Week February 18, 2015. (Photo by Andrew Kelly/Reuters)

Gun enthusiasts look over Smith & Wesson pistols at the NRA Annual Meetings & Exhibits on May 21, 2016 in Louisville, Kentucky. About 80,000 visitors are expected to attend the three-day event. (Photo by Scott Olson/Getty Images)

“In anatomy, heterochromia refers to a difference in coloration, usually of the iris (but also of hair or skin). Although infrequently seen in humans, complete heterochromia is more frequently observed in other species, where it almost always involves one blue eye”. – Wikipedia (Photo by StooMathiesen)

A canine-crazy photographer helped make his dog healthy after seeing him raid the fridge by posing him up with fruit. Scott Cromwell, 43, from Oklahoma City, caught faithful mutt Winston guzzling hot dogs after he looted the refrigerator. Well-trained Winston was then happy to get his five-a-day by taking tongue-in-cheek snaps with red apples, bananas, grapes, limes and orange. (Photo by Scott Cromwell/Caters News)

Models walk in the finale of the Jeremy Scott Fall 2016 collection during Fashion Week in New York, Monday, February 15, 2016. (Photo by Richard Drew/AP Photo)

The Jeremy Scott Fall 2016 collection is modeled during Fashion Week in New York, Monday, February 15, 2016. (Photo by Richard Drew/AP Photo)

Revellers in Newcastle, England on the last Friday before Christmas, December 20, 2019. Black Eye Friday festive mayhem hit the nation; Christmas celebrations kicked off with a bang across the country as revellers flocked to pubs and clubs for the biggest night of the year. (Photo by Scott Heppell/PA Images via Getty Images)