Why does the cat always get it?

Watched The Last Exorcism last night. As PG-13 Blair Witch rip-offs go, it wasn't bad. It has a nicely creepy atmosphere and a good cast. Patrick Fabian is especially good as the charismatic preacher out to prove exorcisms are a sham, and Ashley Bell is convincing as Nell, the girl who may or may not be possessed, even though she looks too old to play a sixteen year old.
The film eschews CGI and extensive makeup (a refreshing change in a horror movie) creating scares by what we don't see, especially in the disturbing scene where a sleepwalking Nell borrows the documentary crew's camera and goes on a naked rampage that includes killing a cat (poor kitty).
Unfortunately, after building up all this suspense, the film fizzles out with a ridiculous left-field ending that is part Wicker Man, part Rosemary's Baby. It really has to be seen to be believed (and be confused by). Worth watching, but don't expect a coherent plot.