Swiss police officers stand beside of mock gates of the NEAT Gotthard Base Tunnel inside the event hall for the upcoming opening ceremony near the town of Erstfeld, Switzerland May 31, 2016. The celebrations of the opening of the Gotthard Base Tunnel will start on June 1, 2016. With a length of 57 km (35 miles) crossing the Alps, the Gotthard Base tunnel is the world's longest train tunnel. (Photo by Arnd Wiegmann/Reuters)

A tourist poses on the glass-bottom bridge at Zhangjiajie Grand Canyon on August 20, 2016 in Zhangjiajie, Hunan Province of China. The Zhangjiajie Grand Canyon's glass-bottomed bridge welcame its trial operation on Saturday and about 8,000 tourists crowded to view the grand glass bridge. (Photo by VCG/VCG via Getty Images)

Devotees attend the annual voodoo festival in Ouidah January 10, 2016. The national voodoo holiday in the West African country of Benin had a distinctively political accent this year as practitioners from Africa and the Americas gathered on Sunday to offer prayers and sacrifices for peace. Hundreds of followers of the traditional religion gathered in the Atlantic coast town of Ouidah, once an important port in the slave trade, to pray for calm during the tiny country's presidential election scheduled for February. (Photo by Akintunde Akinleye/Reuters)

A woman looks at a handgun at the Glock booth at the Shooting Hunting and Outdoor Trade Show, Tuesday, January 19, 2016, in Las Vegas. The SHOT Show, the world's largest annual trade show for shooting, hunting and law enforcement professionals, runs through January 23 and is expected to feature 1,600 exhibitors showing off their latest products and services to more than 62,000 attendees. (Photo by John Locher/AP Photo)

Rioters scuffle with police on a street in Mongkok district of Hong Kong, Tuesday, February 9, 2016. Rioters clashed with police overnight and into the early hours of Tuesday in a crowded area of Kowloon. The unrest started when local authorities tried to prevent street food sellers from operating on Monday night. Activists who are dissatisfied with Hong Kong's administration took part in the clashes, local media reports said. (Photo by Kin Cheung/AP Photo)

Pokot men carry a part of a carcass of a bull killed by a young man during an initiation ceremony in Baringo County, Kenya, January 20, 2016. Far from the bustling city of Nairobi, in an isolated corner of Kenya's Rift Valley, young men from the Pokot community spear a bull in a ceremony called Sapana that takes them into adulthood. (Photo by Siegfried Modola/Reuters)

A Buddhist monk uses a traditional needle to tattoo the body of a man at Wat Bang Phra in Nakhon Pathom province on the outskirts of Bangkok, Thailand, March 18, 2016. Believers from across Thailand travel to the monastery to have their bodies adorned with tattoos and to pay their respects to the temple's master tattooist. They believe the tattoos have mystical powers, ward off bad luck and protect them from harm. (Photo by Chaiwat Subprasom/Reuters)

A photographer takes picture of an automotive model during the 36th Bangkok International Motor Show in Bangkok, Thailand, March 24, 2015. No automotive event is complete without the latest offering of high-end cars and motorcycles, and the obligatory accessories stationed at each booth: nubile, young auto-show girls in skimpy, skinsqueezing outfits. This year's Bangkok International Motor Show did not disappoint, attracting a larger horde of eager, flesh-seeking photographers than actual fans of automobiles. (Photo by Jurnasyanto Sukarno/JG Photo)