Real surprises are rare at the movies these days. Even though I see most films before they’re released, it seems I always know something about a movie before I go in — either I’ve seen the trailer or I’ve read the press notes or I’ve seen something on Twitter or I’ve come across a giant tongue-bath of a story on the cover of “Entertainment Weekly” the week before. Some “surprises” aren’t even surprises any more: No one leaves a Marvel comic-book movie before the teaser scene at the very end we all know is coming.

I’d seen the trailers for Steven Soderbergh’s “Side Effects,” out Friday, and I’d like to nominate them all for Most Ambiguous Trailers That Are Also Incredibly Misleading. And the marketing team in charge of selling the film should take a lot of pride in that (and I’m not being sarcastic).

Walking in, I knew little about what the film is about. Murder! Maybe! And … psychiatric drugs! Possibly! Because the trailers were so nebulous, though — for reasons that are clear once you see the movie — the plot, and all its twists and turns, delivered an unexpected rush that’s rare in a world where God forbid you don’t see “Downton Abbey” live because your Facebook friends will spoil it for you. Unless they acquired season 3 by questionable means, in which case they spoiled it for you months ago.

It seems I always knew that it was a really bad idea for Janet Leigh to take a shower and that Darth Vader was Luke’s father. But with “Side Effects,” I got to gasp and drop my jaw for the first time in a long time. It was a pleasure to be surprised by surprises.