The new Twilight movie has been hit by health fears after cinema-goers suffered seizures.
One scene in the vampire flick has triggered attacks in several viewers since it hit screens worldwide last week.
The latest instalment of the saga, Breaking Dawn: Part One, contains a graphic birth scene.
In it, heroine Bella Swan, played by Kristen Stewart, 21, delivers her husband Edward's baby. Brandon Gephart of Roseville, California, was watching it when he began having convulsions.
His girlfriend, Kelly Bauman, said: "He was convulsing, snorting, trying to breathe. He scared me big time."
The screening was abandoned as paramedics rushed to his aid.
Another man blacked out after watching the same traumatic scene at a cinema in South Jordan, Utah. His wife was shocked when he suddenly began shaking, mumbling and blinking rapidly.
The birth scene contains violent flashes of red, black and white and doctors believe the fast-moving images can trigger seizures in viewers who are prone to photosensitive epilepsy.
Specialist Dr Michael Chez explained: "It's like a light switch going on and off.
"The trouble with cinemas is that it's dark and it's like being hit by a strobe light."
Dr Chez said that any one-off seizures caused by the movie would be unlikely to cause permanent damage.
Similar seizures can be triggered by strobe lighting. Video game designers no longer include strobe effects in their games following a string of complaints.
One episode of the TV spin-off of video game Pokémon, broadcast in the US in the 1990s, caused a wave of seizures in young children.
Twilight, which also stars Robert Pattinson, 25, has been a massive success worldwide with box office takings predicted to top £180m by next week.