Camera trapper Xavier Hubert-Brierre put this large mirror on the side of a road through the jungle in Gabon and left a camera there to record how the animals would respond to their own reflections. A silverback gorilla thought it was seeing another silverback and responded by trying to scare off the potential challenger… (Photo by Xavier Hubert-Brierre/Johns Hopkins University Press)

A competitor gestures as he crawls beneath barbed wire during the Tough Guy event in Perton, central England February 1, 2015. The annual event to raise cash for charity challenges thousands of international competitors in a cross country run followed by an assault course consisting of obstacles including water, fire and tunnels. (Photo by Phil Noble/Reuters)

Nice's Youcef Atal, left, and PSG's Juan Bernat challenge for the ball during the French League One soccer match between Paris Saint-Germain and Nice at the Parc des Princes stadium in Paris, France, Saturday, May 4, 2019. (Photo by Christophe Ena/AP Photo)

Ground personnel tend to actress Yulia Peresild after the landing of the Soyuz MS-18 reentry capsule with herself and director Klim Shipenko of the “Vyzov” (The Challenge) film crew as well as Roscosmos cosmonaut Oleg Novitsky on board, in steppes southeast of Jezkazgan, Kazakhstan on October 17, 2021. (Photo by Sergei Savostyanov/TASS)

West Bromwich Albion's Saido Berahino (front) is challenged by Manchester City's Fernandinho during their English Premier League soccer match at The Hawthorns in West Bromwich, central England December 4, 2013. (Photo by Eddie Keogh/Reuters)

Mark Wagner, the collage artist, challenges viewers to examine their relationship with money and the capitalist society in which we live. Photo: “Way of the Dinosaur”, cut one-dollar bills. (Photo by Mark Wagner)

Lukas Podolski of Koeln is challenged by Philipp Wollscheid of Nuernberg during the Bundesliga match between 1. FC Koeln and 1. FC Nuernberg at RheinEnergieStadion on April 3, 2011 in Cologne, Germany.

Challenger Deep Submersible is shown for the first time at the Virgin Group Media Announcement by the President & CEO of Virgin Airlines Sir Richard Branson at the Newport Harbor Yacht Club on April 5, 2011 in Balboa, California. (Photo by John M. Heller/Getty Images)