Jennifer Carpenter's audition was so convincing and scary that the director decided to cast her right then.
To prepare for her role, Jennifer Carpenter spent hours in a room full of mirrors. She tried out different body positions and facial expressions to see what was the scariest.
Based on the true story of Anneliese Michel, a young German woman who suffered a similar fate to the fictional Emily Rose in the 1970s, and "The Exorcism of Anneliese Michel", an account of the subsequent court case by expert witness Felicitas D. Goodman, an anthropologist called in as an expert on possession. Michel's parents and the two priests who performed her exorcism were prosecuted, though the prosecution asked that the parents be excused from punishment as they had "suffered enough". Ultimately, the accused were found guilty of manslaughter resulting from negligence, and the two clergymen were sentenced to six months in jail (which was later suspended) and three years of probation. The most significant differences are that Michel periodically fasted for several months as part of her exorcism and remained on medication until her death, while the fictional Rose was incapable of eating due to demonic forces and decided herself to stop taking her medication with the consent of her care-providers. The story was heavily adapted for cinematic purposes.
The "silent scream" helped Jennifer Carpenter get the role of Emily Rose. Scott Derrickson found it terrifying in her audition.
The jury was not given scripts so they weren't aware of how the case would turn out. Mary Beth Hurt asked them how they would find Father Moore. The decision was split.