Ben Burtt, the two-time Oscar-winning sound engineer who designed the voices of R2-D2, ET and now the main character in "WALL-E," says his out-of-this-world audio often comes from the most mundane, Earth-bound activities — like a trip to the grocery store.

When he needed the sound of shopping carts banging together for a scene in Pixar's robot love story, Burtt took his 10-year-old daughter to a Safeway, where they put their recorder in a cart and pretended to shop (banging into things in the parking lot for good measure).

But when it comes to making robots emotionally resonant, Burtt bases his ideas on the voice of humans. Very small humans.

"The bulk of the vocals, the expressive vocals, are really sounds that are more like a toddler makes ... kind of the universal language of intonation," Burtt said in an interview aired on AP Radio. "'Oh,' 'Hm?,' 'Huh!,' you know? This sort of thing."

Sometimes, though, finding just the right sound is the product of a happy accident, said Burtt, who's won sound effects editing Oscars for 1989's "Indiana Jones and the Last Crusade" and 1982's "E.T.: The Extra-Terrestrial."

"I'd gotten a big punching bag, a big canvas bag that you normally would beat and box with it, and I wanted to do some impacts," Burtt said. "But I dragged it through the hallway to go to the studio on a rug, and it made a wonderful sound, like a howling wind."

The result: the main component of the sound of a wind storm in the film.

"WALL-E," a Walt Disney Pictures release, opens this weekend.