We spotted Australian actress Sharni Vinson showing off her extremely slender frame in a tiny black bikini in Miami Beach over the weekend. She doesn't look like she has an ounce of fat on her.

The actress wore a string bikini, purple floppy hat and giant yellow sunglasses.

The 30 year old is taking a break from promoting her new horror flick "You're Next" and decided to hit the beach with her friend and fellow actress Kendra Andrews.

Her horror film centers on a gang of masked, ax-wielding murderers who descend upon a family reunion, but an unlikely guest of the family proves to be the most talented killer of all. It opens in theaters Friday, Aug. 23.

Vinson, who dated "Twilight" star Kellan Lutz for two years, has appeared in films such as "Step Up 3-D" and "Blue Crush 2."

See more photos of Sharni at the beach...