rictus

noun

1. A bird’s gaping mouth.
2. The throat of a calyx.
3. Any open-mouthed expression.

   “His face was a rictus of sheer delight.”

   “Amid a thick, bristling beard, a nose like an owl's beak and a mouth whose corners were drawn by a wild-beast-like rictus were just discernible.”

   “A rictus of cruel malignity lit up greyly their old bony faces.”

   “Sword and shield, bone and steel / Rictus grin / Deaf forever to the battle's din”

   “Valves plugs pumps to erase/ rictus from my face.”