Now, if you would rather it look the way I did it, here's how:
I didn't paint the mouth area red before I used the black. I just traced the outline of the mouth with a fine brush and some black cream makeup, then colored it in. (you can find cream makeup at party city or walmart during Halloween time) Then I used the liquid latex (available at, once again, party city or any other SFX makeup store, online, whatever you choose. It's easy to find) to attach the thin strips of tissue paper. The thinner, the better. I just kind of roll them up a bit to make them easier to handle. You may have to reapply latex in order for everything to stick well. I'm sure you can figure it out and do what's most comfortable for you. Then let it dry for a bit.
When the tissue paper is dry, then you'll want to put latex on the back of the teeth and stick them to the tissue paper all around the mouth. Press them firmly or they'll flop over and you'll look like a monster who had a bad trip to the dentist. Next, after the teeth are dry and stuck to the mouth, you can do like the girl in the video did and use foundation to make everything look more natural, or you can skip that and paint the tissue paper with red cream makeup, like I did.
The fun part is the BLOOD! I used plenty of fake blood all around the mouth, dripped some on the teeth, just went crazy with it. It also helps to make it look more disgustingly gory and cover flaws you may have made with the makeup. I also used a thicker kind of blood called Scab Blood but that's only optional. I just used it because it's darker, doesn't drip everywhere, and looks cool. (Note: When you add the blood, you may want to put a piece of paper towel or paper under your face so it can drip onto that and not your table, counter, floor, whatever.)
As for the teeth, I just sharpened the fake nails, filed them to smooth out the edges, and colored them with a mix of brown and black eyeshadows. I painted a bit of fake blood on the underside so they would have a sickly red tint.
But yeah, sorry for rambling. That's just how I did it. ^^ Enjoy! And I do realize that I pretty much told you everything when you could have just watched the video to get all that info, but...hey.