Two attendees compete in the biggest vape cloud competition at the Vape Summit 3 in Las Vegas, Nevada May 2, 2015. According to new research provided to Reuters, youngsters say that performing tricks is one of the top two reasons they began using e-cigs. (Photo by David Becker/Reuters)

Bride Fan Huixiang (front R), a 25-year-old cancer patient, receives flowers from nurses on her bed before her wedding ceremony at a hospital in Zhengzhou, Henan province November 17, 2014. Fan was diagnosed with late stage adenocarcinoma, a type of cancerous tumor, at her thoracic vertebra this June. She and her 24-year-old husband Yu Haining held their wedding ceremony at the hospital on Monday after five years of relationship, local media reported. (Photo by Reuters/China Daily)

The tempestuous stellar nursery called the Carina Nebula, located 7,500 light-years away from Earth in the southern constellation Carina. (Photo by Reuters/NASA)

Steve McCurry has been a photojournalist for over 30 years. He is the recipient of the Robert Capa Gold Medal, the National Press Photographers Award and four first prize awards in the World Press Photo contest. Photo: Afghanistan. (Photo by Steve McCurry)

A collection of Sir Winston Churchill's wartime cigars, including four Romeo y Julieta Cuban Cigars given to Mr Percy Bower, Manager of the cigar department of his suppliers, the Army and Navy Stores to mark the end of the war, are displayed on January 13, 2012 in London, England. (Photo by Matthew Lloyd/Getty Images)

Female Siberian tiger Dasha yawns in the new enclosure at the zoo in Duisburg, Germany, 30 March 2016. The new facility is three times larger than the old one and will be opened to the public on the same day. (Photo by Roland Weihrauch/EPA)

(L-R) Natalie Burns and Taunia Arave battle as referee Nick Stevens (R) looks on during the US National Sumo Championships at the Riviera Hotel & Casino June 24, 2011 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)

Andrew Profilli of Australia bleeds from the head during his 93kg bout against Priscus Fogagnolo of Australia during CFC 18 at Luna Park on August 26, 2011 in Sydney, Australia. (Photo by Ryan Pierse/Getty Images)