A Penarth dance hall has banned chewing gum on the premises because dancers have complained that their feet keep sticking to the floor. (Photo by Richards/Fox Photos/Getty Images). 16th July 1936

The “EMIEW3” robot (R) demonstrates communicating with a visitor during a press preview in Tokyo on April 8, 2016. Japanese electronics giant Hitachi unveiled its humanoid customer service and guidance robot “EMIEW3” and “remote brain” robotics IT platform. (Photo by Toshifumi Kitamura/AFP Photo)

People who fled the violence from Islamic State-controlled northern Syrian town of al-Bab arrive in the rebel-held outskirts of the town, Syria February 3, 2017. (Photo by Khalil Ashawi/Reuters)

This photo taken on August 7, 2016 shows mahjong enthusiasts playing mahjong under water in a swimming pool at a diving club in the Chinese city of Chongqing. Only participants with proper diving certification were allowed to take part in the underwater competition. (Photo by AFP Photo/Stringer)

Robot couple Xiaolan (L) and Xiaotao carry trays of food at a restaurant in Jinhua, Zhejiang province, China, May 18, 2015. The restaurant, which opened on Monday, has two robots delivering food for customers. The robots were designed as a couple, Xiaolan and Xiaotao, according to local media. (Photo by Reuters/Stringer)

A street cleaner demonstrates his martial arts skills in front of a closed shop near Beijing's Tiananmen Square September 2, 2015 as the capital prepares for tomorrow's parade. (Photo by Damir Sagolj/Reuters)

Dancers perform on their way to attend a rally with former President Luiz Inacio Lula da Silva, “Lula”, supporting President Dilma Rousseff in the historic Lapa neighborhood on April 11, 2016 in Rio de Janeiro, Brazil. Brazil's congressional impeachment committee approved the motion to proceed with President Dilma Rousseff's impeachment process today. A full vote by the lower house of Congress on the impeachment is scheduled for Sunday to decide whether she will face trial. (Photo by Mario Tama/Getty Images)

People cross the street in central Pyongyang, North Korea May 4, 2016. (Photo by Damir Sagolj/Reuters)