Knife Thrust

Sometimes a knife isn't just a knife.

Norman (dressed as his mother, Mrs. Bates) kills women with some frequency in his hotel. Which brings up the question: if you're killing people all the time, wouldn't you invest in a better killing tool than a knife? Stabbing someone to death is a messy business (and an uncertain one, as Norman finds at the end when Sam disarms him).

If you're going to be in the business of murder, why not invest in a gun?

Of course, Norman isn't exactly in his right mind (or anyone else's), so you can't expect him to make the best choices. Still, symbolically it's pretty clear why he sticks with the knife. It's because of… sex.

A knife, thrusting in and out of a vulnerable body, is a phallic symbol, bloodily and horribly miming sex. The psychiatrist at the end of the film says that Norman is aroused by Marion, and that his mother personality becomes jealous and kills her.

But you could also see the murder as a completion, or extension of Norman's desire. He looks through the peephole and sees Marion naked…and then he comes into her room and penetrates her, over and over.

Hitchcock Says Enjoy Yourself

And the knifing isn't just about Norman's desire.

You're watching a suspense thriller after all; you're waiting for the gory bits. The knifing is thrilling, satisfying, and stimulating. By linking the murder to sex, Hitchcock is suggesting that he—and you watching—get enjoyment from watching murder onscreen.

And here's the sick thing: we do. Box office returns don't lie. We're addicted to watching gore… in part because we find it totally enjoyable. (Humans are weird.)