Natalie Portman and Bear Grylls Filter Water Through His Underwear

Bear Grylls has a new National Geographic show centering on celebrities doing really gross things in the wild, Running Wild with Bear Grylls: The Challenge. The premiere episode featured Thor: Love and Thunder star Natalie Portman, who joined the survivalist in the slot canyons of Southern Utah. Grylls challenged Portman to help him filter water through his underwear.

During their search for drinking water, Portman and Grylls found a shallow pool of sludgy water. Grylls said they could drink the water, but they have to filter and boil it first. "This water is really full of loads of dead flies and dirt and everything," Grylls said in a clip PEOPLE published last week.

After Grylls and Portman filled up two flasks with water, Grylls struggled to figure out what to use to filter the water. "We could use a sock, but then again, you kinda need your sock," Grylls said before a lightbulb went off in his head. He decided to use his underpants. "We're gonna filter sludge water through underpants?" Portman, who probably wasn't picturing her career going this way after winning an Oscar, asked.

Thankfully for Portman, Grylls didn't need to take his pants off. Instead, he cut the waistband of his underpants and removed what was left of the garment. "I mean it's not going to be perfectly clean," Grylls said, pointing out the obvious for Portman. The Black Swan star thought the plan was "gross," but it worked well enough for Grylls.

Portman's episode aired on Monday and was the premiere for the latest edition of Running Wild. This season will feature an episode with Simu Liu in the Canadian Rockies, another with Florence Pugh in the Costa Rica rainforests, and Ashton Kutcher in the Costa Rica jungles. Anthony Anderson will join Grylls for a trip through the Sierra Nevada mountains, while comedian Rob Riggle visits the Great Basin Desert in his episode. New episodes will air on the National Geographic Channel Mondays at 9 p.m. ET, but Disney+ will post the entire season on Aug. 10.

"I think this one we really push the boundaries in terms of the locations we've gone to and the sort of challenges we've done along the way," Grylls told Forbes of the new series. "You know, we've renamed the show Running Wild: The Challenge just because I think a fun new dynamic is really getting the guests to end up leading a lot of the journey and having to learn these skills and then use the skills on the journey. So that's kind of thrown a whole new dynamic in there."