Ok here are just SOME mouths that I draw sometimes. Sorry for terrible lighting, it's like 2:37 am over here and I don't want to turn on the lights once they're seeping and I left my flashlight in the garage so I'm screwed.

Song: We are the hearts by SuicideSheep

-yelling/snarling/growling?-

Draw a curved line

Continue drawing the line downwards

(Terrible lighting)
Continue drawing the line left and go upwards a little.

Then curve the line upwards almost connecting to the end of the line.

(DA LIGHT OMFG)
Then draw the teeth, the teach can be fangs or missing a tooth it really doesn't matter.

Draw a line in the middle right and curve downwards to the left corner making the tongue. Then shade the back so you can see the tongue and teeth.

-Sticking tongue out-

Draw a curvy line kinda like a mustache.

Then draw a line that goes downward to the center of the mustache line.

Then do the same for the other half.

Draw a line in the middle of the tongue and shade if you want :3

-Realistic lips-
(Sucky)

Draw a circle.

Then draw a curved line just like we used for the other mouth, making it look like a kitty smile.

Now add the v like line on top of the circle.

Continue drawing the line using the v's right side going down connecting with the other line below.

Then do the same for the other.

Draw both sides going downward toward the center. Remember the bottom lip is always thicker than the upper lip.

Then fill in the gap making both lines from both sides go upward making them connect.

Then you shade, also the bottom lip is usually darker for some people.

I really need to work on this book more often XD