The Birds is one of the most terrifying movies ever made if for only one thing - no music. What kind of suspense can you have when you can tell what's going to happen by the tempo of the music? Hitchcock felt the same way. So he took it out altogether. No creepy music leading up to spooky parts that you still jump at any way. Nothing. But. Silence. You don't know what's coming or when. You are just as scared at the people in the movie because those movie lives don't have a soundtrack either. They're hiding out but they can't tell what's going to happen by the sound of the music. Why should you?
Another insanely scary element of this movie - animals acting freaky. And not just, "hey, Fido's getting a little twitchy" but hordes of animals are staring at you and, quite probably, plotting your death. I mean, what would you do if you walked outside your door and blanketing your roof were hundreds of birds? On the power lines, birds. On the lawn, birds. On your car, birds. They're everywhere and you have no idea why and you have no idea what they're going to do.
Until they start attacking. Indiscriminately. And with animals, there isn't a motive, there are no specifics. There's just pure, unadulterated instinct and you're seriously FUBAR because there are way more of them than there are of you. And they peck. To death.
This movie will have you looking at birds in a whole different light. And, really, animals in general. Because who's to say something like that can't happen? Why not? Nature's already pissed at us for what we're doing to the planet. Like the animals won't turn on us next, huh? And what are you going to do? Go duck hunting? The, uh, pecking order (har har) has violently changed and humans are no longer the top beasts in the food chain. Now we're the animals and what we originally knew as animals are the ones hunting us for sport.
If you don't find that extremely freaky, I don't know what'll scare you.
I couldn't find a short original trailer for the movie so this is a fan-made one. Pretty good, actually.