A female forest guard carries a tranquillizer gun in the Gir National Park and Wildlife Sanctuary in Sasan, in Gujarat December 2, 2014. The sanctuary, which is home to Asiatic lions in India, has an area of 1,412 sq km in which female guards were employed for the first time in India in 2007. The guards fetch a monthly salary of around $148 for working almost 12 hours a day, six days a week, said one of the female guards. (Photo by Anindito Mukherjee/Reuters)

People make pictures in a Soviet-era vintage subway car, with a Soviet railways emblem on the side of it, parked in the Partizanskaya subway station in Moscow, Russia, Friday, May 15, 2015. Vintage Soviet-era metro cars were exhibited at the Partizanskaya subway station as part of festivities marking the 80th anniversary of the Moscow subway on Friday. (Photo by Pavel Golovkin/AP Photo)

Soap Bubble Structures by Kym Cox. Bubbles optimise space and minimise their surface area for a given volume of air. This phenomenon makes them a useful tool in many areas of research, in particular, materials science and “packing” – how things fit together. Bubble walls drain under gravity, thin at the top, thick at the bottom, which interferes with travelling lightwaves to create bands of colour. Black spots show the wall is too thin for interference colours, indicating the bubble is about to burst. (Photo by Kym Cox/2019 Science Photographer of the Year/RPS)

A Thai man climbs down from his home in a disused airplane on September 12, 2015 in Bangkok, Thailand. 3 impoverished Thai families have begun living in disused airplanes on a private field. The families, who collect and recycle garbage earning a few dollars a day, can't afford to rent and prefer to stay in the planes. (Photo by Taylor Weidman/Getty Images)

A lioness bares its teeth inside an enclosure after a raid at a zoo-like house on the outskirts of Bangkok, Thailand Monday, June 10, 2013. Thai police and forestry officials searched and seized a number of imported and endangered animals including 14 lions from Africa and arrested the house's owner. (Photo by Apichart Weerawong/AP Photo)

Model Helen Kwok displays the nail art completed by a competitor at the Canada Nail Cup in Vancouver, Monday, February 16, 2015. Nail artists competed in multiple categories at the event, which according to organizers is the only nail competition in the country. (Photo by Darryl Dyck/AP Photo/The Canadian Press)

Rock and roll musician Elvis Presley during a press conference after his first performance at the International Hotel in Las vegas, Nevada on August 1, 1969. (Photo by Michael Ochs Archives/Getty Images)

Damaged vehicles sit on Yeongjong Bridge in Incheon, South Korea, Wednesday, February 11, 2015. Two people were killed and at least 42 were injured on Wednesday after a pileup involving about 100 vehicles in foggy weather on the bridge near the Incheon International Airport, South Korean officials said. (Photo by Suh Myung-gon/AP Photo/Yonhap)