Kristen Stewart felt like "an absolute nutcase" during the birth scene in The Twilight Saga: Breaking Dawn - Part 1.
The American actress reprises her role as Bella Swan in the movie, which is the first instalment of the two-part finale of the popular vampire film series.
The film sees Bella and vampire Edward Cullen - played by Robert Pattinson - marry and have sex for the first time. Bella falls pregnant after their night of passion, and gives birth to a half-vampire baby.
The PG-13 rating limited filming with regard to the intense birth scene.
"That's what I'm really disappointed about - and I've talked about it with Bill [Condon, director]" Stewart told Entertainment Weekly.
"It was more sympathetic or something when I played the scene with less energy, and it made it easier for him to tell the story. But in the book, Bella is screaming, 'NOOOOO!'. And I did it like that - crazy and Exorcist-like.
"I was going for this weird mix of turning into the most feral mother you can imagine and also fighting for my own life. I mean, I was a nutcase. I was an absolute nutcase."
Meanwhile, Pattinson says he was "crying" with laughter during the birth scene because his face was covered in strawberry jam.
Despite the gory storyline, the British actor couldn't help seeing the funny side when he was shooting the scenes.
"So someone said, 'You give her a caesarean by chewing through her,' and I was like, 'Um, okay!"' Pattinson told UK TV show Daybreak.
"We had a midwife and a doctor there to ask what the scientific feasibility of it all was and they were so confused as to why they were there.
"It looks so extreme in the movie and when we were doing it I was literally crying with laughter. There was this cream cheese and strawberry jam which I had to wipe on my face and then come up again for the shot. It was the most ridiculous and surreal thing I have ever done."
Pattinson admits he was lost for words when he discovered what happens in the film. The 25-year-old actor has revealed one of the crew explained what was in store for Edward and Bella before he had a chance to read the script.
"When someone summarised the story for me before I read the book or the script I was literally like, 'What?' Because Bella has this diamond-heart uterus because it's a half-vampire baby and the only thing that can break into it is vampire teeth," he explained.
Taylor Lautner - who plays werewolf Jacob Black in the series - agrees with the sentiment. However, the actor is still impressed with how the scene turned out.
"I do still love the birth scene," he added.
"I know it's frustrating that some things aren't in there."
Pattinson and Stewart's intimate scene was also edited with the film's young audience in mind.
The pair were disappointed that the passion was cut out at times.
"There's a version where it was really intense," Pattinson revealed. "Cinematically, cut all together, it's awesome. But we didn't really do that scene," Stewart added, before Pattinson chimed: "And when we did, they kept telling us to stop."