Yawn
A gaping movement of the mouth. In a first stage, the mouth is partially opened, forming an oval shape. Then the head is tossed back and the mouth open to the fullest extent before to be rapidly closed with head returning to the normal position.
Thierry, B., EL, B., Baker, S., Matsumura, S., Muroyama, Y., TG O, B., ... & Watanabe, K. (2000). The social repertoire of Sulawesi macaques. Primate Research, 16(3), 203-226.