London: Actress Jennifer Aniston reportedly freaked out on her movie set, after her co-actor Sam Worthington played a prank on her.

The 45-year-old `Friends` star got scared at the sets of her new movie `Cake` about a scene where she visits a woman`s grave, reportedly.

"She kept telling everyone she couldn`t wait for the scene to be done and gone, because the graveyard gave her eerie vibes. That gave Sam the idea for his prank, so he talked a sound technician into concealing a microphone on the grave right next to where Jennifer was filming!" a source said.

Aniston is playing a character haunted by the shocking suicide of a woman in her chronic pain support group in the movie. "So just as the star delivered her final lines, a soft female voice whispered, `Jennifer!`

"Cast and crew fought to suppress giggles as Jen turned ghost-white and gasped, `Did you all HEAR that?... Someone was calling my name!` Everyone played dumb, until the voice called out again and Jen screamed `There, did you hear that? Who`s doing that?`" the source said.

Aniston has apparently vowed to avenge the prank. "Everyone realized Jen was truly scared, so they decided to blow the whistle before they got blamed ? and told her she`d been pranked by Sam. Jen vowed revenge ? warning Sam to watch his back!" the source said. (PTI)