Young girls practice acrobatic skills in the Sichuan Provincial Art School July 14, 2008 in Chengdu of Sichuan Province, China. (Photo by China Photos/Getty Images)

Young gymnasts practice pull-up on a bar at a gymnasium of a sports school in Jiaxing, Zhejiang province April 11, 2015. (Photo by William Hong/Reuters)

Dancers at the Windmill Theatre in London, England practice a routine wearing gas masks and hard-hats with their costumes, 1940. (Photo by Hulton Archive/Getty Images)

“APOPO’s Training Center, situated on Sokoine Univeristy of Agriculture (SUA) in Tanzania, was established in 2000 to accommodate training and testing of mine detection rats in near-to-real conditions”. – APOPO

Photo: MDR (Mine Detection Rat) learn to look for mines. (Photo by APOPO's HeroRATs)

An invited guest enjoys a private listening experience of a test unit of the Sennheiser HE 1 sound system, which is expected to retail for about S$77370 ($55000), in a hotel suite during the CanJam headphone and personal audio expo in Singapore February 21, 2016. (Photo by Edgar Su/Reuters)

Clouds reflect off the water as they pass over while SpaceX prepares their super heavy-lift Starship SN8 rocket for a test launch this week at the company's facilities in Boca Chita, Texas, U.S. December 1, 2020. (Photo by Gene Blevins/Reuters)

A medical worker in protective gear sprays mist on her colleague during a hot day at an outdoor clinic for coronavirus tests at a public health facility in the southwestern city of Gwangju, South Korea, 05 June 2020. (Photo by Yonhap/EPA/EFE)

A U.S. Army crew chief flying on board a CH-47F Chinook helicopter observes the successful test of flares during a training flight in Afghanistan, March 14, 2018. (Photo by Tech. Sgt. Gregory Brook/Reuters/U.S. Air Force)