"It was really fun — it felt very natural — it felt more natural than actually doing romantic comedies, which is weird, but it was great," Hudson told FOX News.
Hudson says she wasn't a believer in black magic, but one scene may have changed her mind.
"There were a few spooky things — when I did the scene with John [Hurt] — the spell — I got a little bit of the jitters. It felt a little like we were doing a little science and inviting things that maybe we shouldn't have been inviting."
The film revolves around hoodoo, or black magic that's a lot like voodoo with the religious element removed.
But the movie is getting the most buzz over its surprise ending.
"When I read it the end was so unexpected and rare for a Hollywood studio to be doing a big movie that has an ending like this, and I just went, 'Well, that's totally refreshing,'" Hudson said.
In the movie, Hudson's character Caroline goes to work for Violet (Gena Rowlands) (search), a strange old lady who lives in a big, crumbling old house way out in the Louisiana bayous where all the mirrors have been removed.
Caroline has been hired to take care of Violet's husband Ben (John Hurt (search)), who is supposedly paralyzed and near death after a stroke.
But Caroline soon finds notes from Ben to "please help me" — and a locked room in the attic with the belongings of two former black servants who were lynched for being witch doctors.
According to the New York Post's Lou Lumenick, at this point, "Any reasonable person would flee, but because she feels guilty about her own father's death, Caroline is studying to become a practitioner in the black arts to rescue Ben.
"She seeks help from a pair of familiar stereotypes: Violet's lawyer — who might as well have "do not trust me" engraved on his forehead (Peter Sarsgaard (search)) — and her perky black former roommate (Joy Bryant)."
Lumenick adds: "Kate Hudson's flatlining career isn't going to be resuscitated by "The Skeleton Key," a hokey Southern-brain-fried thriller."
FOX News' Bill McCuddy was also scared away.
"I've just seen one of the summer's new comedies. Unfortunately, this is humor of the unintentional kind. Because 'The Skeleton Key' is supposed to be a thriller. At the end I was thrilled to leave."
FOX News' Mike Waco and Bill McCuddy and the New York Post's Lou Lumenick contributed to this report.