How to create an eating animation? Similar to This?

I have a 3d character with a very similar setup, she’s 3d but her mouth is 2d, I saw this video recently the character is 3d and the face is 2d (at least I think it is) I can’t really find any animation tutorials on how to accomplish this effect of the character eating. Any tips? I’ll post my model later if that will help answer. This is the video I would like to mimic.

Expressions sprite sheet with uv offset.

It could also be animated decal projected onto the face.