A genetically engineered featherless rooster struts around the campus of the Hebrew University of Jerusalem's Department of Agriculture May 22, 2002 in Rehovot, Israeli. After two years of research, departmental scientists announced the naked chicken, as it has been dubbed, as a low calorie bird because the lack of feathers means the chicken has less fat. It also matures earlier than its feathered counterparts. (Photo by Moshe Milner/GPO/Getty Images)

Participants run at the “Half-Naked Marathon” at Olympic Forest park in Beijing, China, February 28, 2016. This annual running event which requires participants to run half-naked, was organized to promote environmentally friendly lifestyles. (Photo by Kim Kyung-Hoon/Reuters)

This brave swimmer certainly has a brrracing workout each weekend she skinny dips in one of the coldest rivers in Europe which regularly plummets to temperaturess of –9C. Inna Vladimirskaya, 32, strips off on the banks of the Dnieper river, in Kiev, Ukraine, every Sunday morning, and takes a swim after jogging along the snowy banks of the river in the nip. (Photo by David Tesinsky/Caters News Agency)

A competitor reacts as she emerges from the water during the Tough Guy event in Perton, central England, January 26, 2014. The annual Tough Guy race – “the toughest race in the world” – at Perton in Staffordshire. Tough Guy claims to be the world’s most demanding one-day survival ordeal. First staged in 1987, the Tough Guy Challenge has been widely described as one of the hardest races of it’s type with up to one-third of the starters failing to finish in a typical year. (Photo by Darren Staples/Reuters)

A competitor makes their way through fire as they take part in the Tough Guy endurance event near Wolverhampton, central England, on January 27, 2019. The Tough Guy event challenges hundreds of competitors to run a gruelling course whilst negotiating up to 300 obstacles including water, fire, and tunnels. (Photo by Oli Scarff/AFP Photo)

Children react as they celebrate Guy Fawkes day in Soweto, South Africa, on November 5, 2014. (Photo by Siphiwe Sibeko/Reuters)

A competitor reacts as she takes part in the “Tough Guy” adventure race near Wolverhampton, central England, on January 29, 2017. The Tough Guy event, which is being held for the final time in its 30th year, challenges thousands of competitors to run a gruelling course whilst negotiating over 200 obstacles including: water, fire, and tunnels. (Photo by Oli Scarff/AFP Photo)

A competitor reacts ahead of Tough Guy Mudathon event in Perton, Britain, 04 February 2018. The original event which started in 1987 raises money for charity and challenges thousands of international competitors with a cross-country run followed by an assault course consisting of 20 obstacles including water, fire and tunnels. (Photo by Nigel Roddis/EPA/EFE)