Podcaster Lex Fridman took to Twitter to share a video of him training in jiu-jitsu with Meta's billionaire CEO Mark Zuckerberg amid Elon Musk's cage fight challenge. "It's inspiring to see both Elon and Mark taking on the martial arts journey," he wrote. Brazilian jiu-jitsu is a form of Japanese martial art which involves grappling, ground fighting, and submission holds.