noun / verb
mouth
MOUTH/maʊθ/
The opening in the face used for eating and speaking.
The person's mouth is relaxed and slightly open between the lips.

Etymology
Old English muþ already meant the oral opening and could also describe an opening, door, or gate. The facial sense is inherited directly; the word's deeper origin is disputed.
In context
her mouth is frowning too I think she's feeling frustrated
More examples
- Sunlight reaches only a few feet inside the mouth of the cave.
- He mouths “thank you” through the window without making a sound.
- She mouths an apology, but she clearly feels no regret.
- He gets in trouble for mouthing off to his teacher.
Forms
mouth · mouths · mouthed · mouthing
mouthful noun — An amount that fills the mouth.
mouthy adjective — Tending to speak rudely or disrespectfully.