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Shocked families at Nottingham's Cineworld in the UK had to rush their children out of the auditorium as they realised that the wrong film was being projected.
But not before a scene at the very start of the film - featuring a bloodied female corpse being thrown at the camera – upset children as young as five, among around 25 families watching.
Natasha Lewis of Bulwell in Nottingham, who took her eight-year-old son Dylan to the screening, said: "They started playing the movie and I thought - this doesn't look right. And then I recognised the opening sequence as a flash back to the first movie, which I saw a couple of years ago.
"It opens on the most terrifying scene in the first film - where a body shoots full pelt towards the camera. It's enough to make grown men jump, so you can imagine the terror in these young faces.
"Everybody just scrambled for the exits, all you could hear were children crying and screaming. Everyone was very upset.
"I've watched a few horror films in my time but the 'Paranormal Activity' films are the scariest since 'The Exorcist'.
"It was only about two minutes worth of the film but it was enough to scar them for life. There were parents and kids in there, including some children who were younger than Dylan.
"The cinema needs to check the film before sending everyone in so they don't make this mistake again. I'm disgusted about it, mistakes like this simply should not happen."
A spokesperson for Cineworld said: "We have investigated the incident and can confirm that this was a technical error with the projector and apologise sincerely to the families.
"All customers who were affected by the incident were offered refunds and complimentary tickets. We also invited customers to watch the screening of Madagascar 3 half an hour later.
" We take matters such as this very seriously and are currently working with technicians to ensure this does not happen again."Related Video: Watch the trailer for "Madagascar 3"