Four-man bicycle is powered by five chains and has brakes on both its wheels, 1948. The bike was built by Art Rothschild (top position) who broke three ribs while learning how to ride it. (Photo by Wallace Kirkland/Time & Life Pictures)

A participant learns to throw a grenade during a military exercise for civilians conducted by members of the Georgian National Legion paramilitary volunteer unit amid threat of Russian invasion in Kyiv, Ukraine on February 4, 2022. (Photo by Serhii Nuzhnenko/Reuters)

Participants learn how to survive in the wild, including tips on how to make it through a zombie invastion at a “Zombie First Responder” course March 11, 2012 in Sandy, Oregon. In an intensive 2-day curriculum participants train in everything from wilderness and urban survival, nerf or nerd weaponry, stealth and evasion, and proper zombie “disposal”. (Photo by Natalie Behring/Getty Images)

A cat stretches on top of dried seafood in a shop in the Sheung Wan district of Hong Kong on August 7, 2020. International Cat Day, celebrated on August 8, is a day to raise awareness for cats and learn about ways to help and protect them. (Photo by Isaac Lawrence/AFP Photo)

“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)

German field telegraph operators at work in Warsaw. (Photo by Hulton Archive/Getty Images). 1st October 1914

An East German civilian (L) shows an East German customs officer the contents of his Trabant (auto) at checkpoint Potsdamer Platz in East Berlin in this November 24, 1989 file picture, as East Germany enforcing stringent customs controls to avoid smuggling. (Photo by Reuters)