If you can’t tell why, tilt your screen down.
Then say, “Whoa.”
If you haven’t seen the movie, stop reading immediately and go do so. You will be the better for it, and this poster will make a lot more sense to you.
And though I rarely say this, I’d advise you see the movie before reading the book. This is one of those exceptionally rare instances in which the film is much better than the book.