How do you edit the inside of the mouth?

[Naku-Chan]

I noticed there are options to edit the inside of the mouth but when I do I can't see the changes. The models mouth is always closed. It seemed like in earlier versions there was a way to view different expressions. I don't know if I just can't find it or what but in that they showed the mouth open. Am I missing something? I just started messing around with this today.

[KaitoSai]

in the face tab (where you can also find mouth inside, or eyes, all of that) you scroll down to the bottom of the left sidebar
at the bottom of the left sidebar in the face tab is the expressions editor

open mouth expressions are "happy", "surprised", "A", "E"

if you start messing around wth the expressions setting, just as a warning with the closed eyes, closed eye left, and closed eye right:
do not change anything in the face but the eyes. only adjust the eyes.
if your neutral expression mouth looks different thats fine, dont try to fine tune the mouth in the close eyes menu.
the reason is, when your model is blinking it adds the closed eyes to the expression the model has right now. if a smiling model blinks with a closed eye expression that also messes with the mouth it will look cursed as heck.