VIDEO : Christina Aguilera Surprises Strangers With A Serenade And Free Donuts

Christina Aguilera pranked visitors at Randy's Donuts in California as part of a new segment on ABC's "Jimmy Kimmel Live" called "Undercover Sing."

Hidden cameras were set up inside the shop to capture the reactions from customers, who had no idea that the singer was in a room watching them.

As people approached the counter, Aguilera belted out personalized songs (to the tune of her hits, like "Genie in a Bottle" and "Survivor") based on their appearances.

She then stepped out of a curtain and appeared with a microphone in one hand and donuts in the other for the delighted customers.