Talk Like Snape
I already know this is gonna be one of the longest ones, but not longer than the Walk Like Snape. Well, you shouldn't expect any different, because learning to talk like Snape is an intricate process.
Voice
I always refer to Snape's(or Alan Rickman's) voice as "The Voice," because it's the best voice ever. And the sexiest. It's dark, silky, and commands your attention. He can use it to arouse you, or lull you to sleep if he wants. It's also pretty scary sometimes.
Now, the major part of getting his voice right is the accent. We only know Snape's real voice by the movies, and since I'm pretty sure J.K. Rowling had Alan Rickman in mind when she wrote his character, I'm basing this off Alan Rickman's voice. He has a west London accent, since he was born in Hammersmith(coincidentally the same city Daniel Radcliffe and Hugh Grant were born), but to me, it sounds a bit like a Suffolk accent. I don't know, maybe I'm just imagining it. But, in Suffolk there's a city called Snape. So that's... pretty awesome. I want to live there.
So, you could either get accent lessons, or just watch tons of Rickman and Grant movies and go from there. Unless you're lucky and already have a West London accent. Then, of course, there's the deepness of his voice.
His voice is so deep, you can get lost in it. Try to develop somewhat of a monotone voice, but at the same time, you shouldn't sound bored. Does that make sense? It should be silky, cold, and striking. Put emphasis on any harsh word and the end of sentence. But you should always sound annoyed, and never let any softness or warmness into your voice. It should either be an angry, annoyed, or sarcastic tone. That's what makes Snape so badass.
Sometimes, though, when he's especially angry, his voice gets a bit nasal. You'd imagine, with the size of his nose, that he'd be a nose-breather. It's actually quite easy to get your voice nasal if it doesn't already do that when you get mad. I don't know how to explain it, though. It's just the kind of thing that seems to have a muscle on its own, and you're not really sure how you control it. Like how I can cross my eyes without looking at my nose, just by straining some muscle in my eyes. I suppose it has something to do with the way you intake air when you talk. It's somwhat high-pitched, and just focus your voice into nose.
Mouth Movement
You should have noticed that Snape doesn't move his mouth much. He avoid opening his mouth too much if he can help it, as most syllables can be pronounced without much lip movement. He speaks inside his mouth, and often through gritted teeth.
To others, it should look as if you aren't speaking at all. If you're whispering because you don't want something to be heard, they won't have any idea you're even talking. As much as he prefers to keep his mouth closed, though, he opens it huge when he yells. In the Chamber of Secrets when he's yelling at Ron and Harry, his face is screwed up with anger and his mouth is more open than ever.
Though he doesn't often open it vertically much, his mouth becomes quite wide, but usually only on one side. Watch the Chamber of Secrets, the part where Snape's dueling Gilderoy Lockhart. I'm sure we all remember how he says "Expelliarmus" rather strangely... That's what I mean.
Also, when making certain sounds, you should not that he does a sort of "duck lips" thing. I don't know why, but it's just really adorable. Watch some Snape scenes, and you'll get the picture.
Okay, so you guys can't control what voice you're born with. Some of us have high-pitched voices that we can't change, and maybe the best you can do is change your tone of voice. But the way Snape talks is unforgettable, and people will recognize it when they hear it.