Hotel staff practice self-defence skills after a training session given by team member of Special Weapons and Tactics (SWAT) team, in Hangzhou, Zhejiang province, April 7, 2016. (Photo by Reuters/Stringer)

Bjorn, aged 5, smiles as he poses with a Owl butterfly during an event to launch the Sensational Butterflies exhibition at the Natural History Museum in London, Britain March 23, 2016. The exhibition opens to the public on March 24 and runs until September 11. (Photo by Dylan Martinez/Reuters)

Workers hold an 80 Kg Paiche (Arapaima gigas) to return it to a pool at a breeding farm in Nueva Loja, Ecuador, March 25, 2016. (Photo by Guillermo Granja/Reuters)

Joshua Patino stands on a ladder to put finishing touches on a giant dinosaur exhibit at PAX East in the Boston Convention and Expo Center, Thursday, April 21, 2016, in Boston. PAX East, an annual celebration of gaming culture, is expected to draw tens of thousands of visitors Friday through Sunday. It's a place where serious gamers can preview unreleased video games and devices, compete in tournaments, hear live music and meet others for whom gaming is a way of life. (Photo by Elise Amendola/AP Photo)

Taiwanese-US artist Chin Chih Yang poses for a photograph with 30,000 aluminum cans after his performance called “Kill Me or Change” in Taipei, Taiwan, 23 April 2016. “Kill Me or Change!” is a performance piece that aims to raise awareness of the benefits of recycling and, encourage people to recycle to conserve resources. (Photo by Ritchie B. Tongo/EPA)

Members of the Royal Navy respond to a simulated fire in a Vanguard-class submarine control room training facility at Clyde naval base in Faslane, Scotland on January 21, 2016. (Photo by Photograph: Danny Lawson/PA Wire)

A Libyan fireman stands in front of smoke and flames rising from an oil storage tank at an oil facility in northern Libya's Ras Lanouf region on January 23, 2016, after it was set ablaze earlier in the week following attacks launched by Islamic State (IS) group jihadists to seize key port terminals. (Photo by AFP Photo/Stringer)

View of an egg fried on the pavement in Pozo Hondo, Santiago del Estero, Argentina on January 23, 2016, while the real feel was 57 degrees Celsius. Pozo Hondo's Mayor Claudio Nicolau fried an egg on the pavement of the main square of the city Saturday. (Photo by AFP Photo/Stringer)