National Guardsmen are put through riot training in Boston's Commonwealth Armory on Friday, October 18, 1974. Massachusetts Gov. Francis W. Sargent called up the guard to quell school violence, but the city has been relatively calm and the guard has remained in the armories. (Photo by JWG/AP Photo)

Arizona Cardinals cheerleader Claire Thorton, center, smiles as Air Force Capt. Eric Straub proposes to her during the first half of an NFL football game against the Washington Redskins, Sunday, October 12, 2014, in Glendale, Ariz. Thorton accepted the proposal. (Photo by Rick Scuteri/AP Photo)

People in costume take photos during a Halloween event on October 31, 2015 in Lan Kwai Fong, Central District, Hong Kong. Halloween, a named taken from 'All Hallows' Even' falls on the day before All Saints' Day on November 1, a holiday when Christians remember their deceased loved ones. (Photo by Jerome Favre/Getty Images)

Juno, a Beluga whale, greets a young viewer at the Mystic aquarium in Connecticut, USA on December 5, 2015. (Photo by Tim Clayton/Corbis)

People feed the birds in Battery Park in the Manhattan borough of New York, December 18, 2014. Hart has been feeding the birds three times a week for the last three years. (Photo by Carlo Allegri/Reuters)

A mechanical horse-dragon made of wood and steel is presented to the public in Nantes, western France on August 26, 2014. This horse-dragon, created by the French artist Francois Delaroziere of “Les Machines de l'île” (The Machines of the Isle), is the hero of the show "Long Ma" which will be presented in Beijing on October 17, 2014 as part of the fiftieth anniversary of the relationship between France and China. (Photo by Jean-Sebastien Evrard/AFP Photo)

A passenger not wearing pants sits in a subway train during the “No Pants Subway Ride” in Prague, Czech Republic, January 10, 2016. The event is an annual flash mob and occurs in different cities around the world in January, according to its organisers. (Photo by David W. Cerny/Reuters)

Women wearing traditional dresses with pins of pictures of former North Korean leaders Kim Il Sung and Kim Jong Il welcome foreign reporters on a government organised visit to the Kim Jong Suk Pyongyang textile mill in Pyongyang, North Korea May 9, 2016. (Photo by Damir Sagolj/Reuters)