Joseph Gordon-Levitt regaled David Letterman with quirky family stories on Wednesday night's "Late Show."
"My older brother never did the acting thing. He spins fire for a living," Gordon-Levitt said. "It's fire on a ball and chain, and he spins them around in cool patterns."
"If you feel a -- certain way," he added knowingly, "it looks cool. To your eyes." Letterman and the audience responded with laughs.
"He's one of the best in the world. Burning Dan," Gordon-Levitt said of his psychedelic brother.
The young actor appears alongside Leonardo DiCaprio in "Inception," a surreal sci-fi written and directed by Christopher Nolan ("The Dark Knight," "Memento"). Gordon-Levitt first rose to fame when he starred as an alien on "3rd Rock from the Sun" in 1995, at age 15.
Earlier in the show, Letterman showcased offbeat toys for summer, including a giant, inflatable orb that you crawl into and then move about like a hamster. It seemed similar to Zorbing, an extreme "sport" originating in New Zealand.
After seeing Letterman roll around the studio in the big ball, Gordon-Levitt begged, "Can I get in that hamster ball thing?"
"It's deflated," a stage hand responded off camera. We cut to, and hold on, a sad shot of the collapsed, plastic pile, shoved into a corner. "Awww," the audience moaned.
Regarding the weightlessness effects in "Inception," Gordon-Levitt said, "They didn't fake it digitally. Christopher Nolan is a big fan of reality. So they built a big corridor that rotated 360 degrees... the floor becomes the wall, the wall becomes the floor."
He explained that wires suspended the actors in mid-air.
The film takes place in people's dreams, and characters "go inside" these dreams to extract information. The dreams are also "shared" -- that is, all the characters can be in the same dream. And outside factors can affect them while they're in this state.
"If we're all in a van getting away from bad guys, asleep and dreaming, and the van goes off in this embankment and we're spinning around in the van, we spin around in the dream," Gordon-Levitt said. "Gravity goes all crazy."
The actor also talked a bit about his earlier years: "I was six when I got my first job. My parents didn't pressure me in the slightest... my mom drove me to auditions every day and I did maybe one or two a day. It's been 23 years, and now I'm here," he said of his "Late Show" appearance. "It's crazy."
"You could do better," Letterman joked.
"I don't think so, man."
After the interview, life was re-breathed into the giant hamster ball, and an already giddy Gordon-Levitt got to take it for a spin outside the theater.