Men slide in the mud during the Boryeong Mud Festival at Daecheon Beach in Boryeong, South Korea, Saturday, July 22, 2017. The 20th annual mud festival features mud wrestling and mud sliding. (Photo by Ahn Young-joon/AP Photo)

A woman walks past a stall at a market in Banjul, Gambia December 15, 2016. (Photo by Afolabi Sotunde/Reuters)

A man covered with mineral-rich mud smiles on a bank of lake Tus in Khakassia region, southwest of the Siberian city of Krasnoyarsk, Russia, July 16, 2016. (Photo by Ilya Naymushin/Reuters)

Thai emergency staff help the injured after the scene of an explosion near Erawan Shrine, central Bangkok, Thailand, 17 August 2015. An explosion in a busy commercial district in the Thai capital killed at least 15 people. Witnesses said the explosion happened around 7:15 pm (12:15 GMT) at the Rajprasong Intersection, a business area famous among tourists and locals for a revered Hindu shrine. (Photo by EPA/Stringer)

A woman touches a robot at the 2018 World Robot Conference in Beijing on August 15, 2018. The conference will be held from 15 to 19 August and will include a conference on robotics, an exhibition and a robot competition with the participation of robotics enterprises to showcase their robot products. (Photo by Wang Zhao/AFP Photo)

An artist performs with a lion during the presentation of the new international show “Extreme arena” at the Ukrainian National Circus in Kiev, Ukraine, 15 September 2016. The show will be staged from 15 September to 11 December 2016. (Photo by Roman Pilipey/EPA)

Two F-15E Strike Eagles wait to receive fuel from a KC-135R Stratotanker during exercise Red Flag 15-1 on their way to Nellis Air Force Base, Nev., Jauary 23, 2015. The F-15s are assigned to the 4th Fighter Wing. U.S. (Photo by Airman 1st Class Aaron J. Jenne/Reuters)

A resident looks at a parade marking the 496th anniversary of Panama City, Panama August 15, 2015. Modern-day Panama City includes the historical ruins of the original Panama Viejo settlement founded on August 15, 1519 by Spaniard Pedro Arias Davila, according to local media. (Photo by Carlos Jasso/Reuters)