Long before Amy Winehouse was a music icon and tabloid staple, she was just an ordinary teenage girl at a birthday party -- with a voice so incredible, even then, that it could hold a whole room in thrall.

In this clip from "Amy," the documentary about Winehouse's life and tragic death, a 14 year-old Amy is seen at the birthday party of her friend Lauren Gilbert, late in the evening after most of the other guests have already gone.

At first, it's just a sweet, candid, behind-the-scenes glimpse of Amy before she became a star, as she and the other girls goof around on a staircase and try to goad Lauren into eating some birthday candy. But when one friend starts to sing "Happy Birthday," out comes that voice -- and all the giggling teenagers fall silent, and listen.

"Amy" releases in the U.S. July 3.