Karis, an 8 week old lion cub, growls at a pumpkin as she explores a Halloween treat put in her enclosure by staff at Blair Drummond Safari Park near Stirling, Scotland, Tuesday, October 29, 2013. (Photo by Andrew Milligan/AP Photo/PA Wire)

A murmuration of starlings above the the small village of Rigg, near Gretna, in the Scottish Borders, on November 25, 2013. The weight of the resting birds on power lines caused some power localised power outages in the village. Still one of the commonest of garden birds, its decline elsewhere puts it on the Red List of endangered species. (Photo by Owen Humphreys/PA Wire)

Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)

Syrian refugees sit behind barbed wire as they wait to cross into Macedonia at the Greek-Macedonian border, near the village of Idomeni, August 21, 2015. (Photo by Yannis Behrakis/Reuters)

Handout photo issued by Easyart of an experimental motorcycle as an archive of weird and wacky innovations has been unearthed by an amateur historian as he trawled through a collection of images spanning the last 100 years. (Photo by Easyart/PA Wire)

The northern lights, or aurora borealis, appear in the sky over the Bamburgh lighthouse at Stag Rock in Northumberland, England on September 28, 2016. (Photo by Owen Humphreys/PA Wire via ZUMA Press)

Abbey Clancy attends Lifetime's launch of Britain's Next Top Model airing tonight at 9pm on Lifetime on March 16, 2017 in London, England. (Photo by PA Wire)

Young performer at The Lal Kach festival, an event well known in the local community for more than hundred years in Dhaka, Bangladesh on April 13, 2017. (Photo by Mushfiqul Alam/ZUMA Wire/Rex Features/Shutterstock)