"'Warm in Toronto,' that's the name of this segment," Johansson told ET.
In the movie, a koala (McConaughey) enlists the help of his friends to host a singing competition, hoping to drum up business for his theater.
Johansson plays a punk rock porcupine, whose voice is bigger than her stature.
"I don't really know what she sounds like," Johansson said. "She's sort of just like loud and proud."
Witherspoon plays a pig, who beautifully belts out Katy Perry's "Firework" in the movie, but the actress told us that her singing at home isn't always welcomed by her three children, 17-year-old Ava, 12-year-old Deacon and 3-year-old Tennessee.