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, reported Showbizspy.
"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.