For want of anything better to do, I watched The Exorcism of Emily Rose on the plane on the way back from Sydney; and a fine piece of nonsense it was too, graced by Laura Linney looking pained as it began to sink in just what a farrago she was starring in.
There's one overwhelming question about demonic possession: what does the devil get out of it? If you're the devil, there must be more fun to be had than spending precious days inhabiting some poor pathetic body which you proceed to rack into unlikely poses, preferably in the vicinity of someone holy. Then the next dance move: twist the head round, bulge the eyes out of its little head, and bellow in ancient tongues (the clever polyglot you are!) in a very deep voice. The possessee (in this case Emily Rose) doesn't appear able to wreak very much real physical damage on anyone: it's all a bit ineffectual in the end and there is still plenty of room for doubt: look, forget possession, maybe she was just a bit mental.
So why is the devil not sneaking in to Versace in invisible guise and stealing armfuls of jewel-coloured silk dresses to hand out to the poor (true cruelty), or shaving Paris Hilton's head in the dead of night, or painting graffiti on the walls of St Paul's (Romanes eunt domus perhaps)? That's how to get people's attention.