I could not hear a sound, but through my glasses I saw the thin arm extended commandingly, the lower jaw moving, the eyes of that apparition shining darkly far in its bony head that nodded with grotesque jerks. Kurtz - Kurtz - that means 'short' in German - don't it? Well, the name was as true as everything else in his life - and death. He looked at least seven feet long. His covering had fallen off, and his body emerged from it pitiful and appalling as from a winding-sheet. I could see the cage of his ribs all astir, the bones of his arm waving. It was as though an animated image of death carved out of old ivory had been shaking its hand with menaces at a motionless crowd of men made of dark and glittering bronze. I saw him open his mouth wide - it gave him a weirdly voracious aspect, as though he had wanted to swallow all the air, all the earth, all the men before him.
Kurtz's gaping mouth recalls H. G. Wells' description of a momentary impression Mrs Hall has of the title character in The Invisible Man:
... for a second it seemed to her that the man she looked at had an enormous mouth wide open, - a vast and incredible mouth that swallowed the whole of the lower portion of his face. It was the sensation of a moment: the white-bound head, the monstrous goggle eyes, and this huge yawn below it.
Similarly, Edvard Munch's painting The Scream (1893) shows a contorted face with a gaping mouth.
Inspired by Munch's The Scream, Wes Craven's 1996 movie Scream features a killer wearing a halloween mask that also has a gaping mouth.
Scream (1996) Dir. Wes Craven
Another screaming mouth can be found in Francis Bacon's 1953 Study After Velazquez's Portrait of Pope Innocent X.
Study After Velazquez's Portrait of Pope Innocent X (1953) Francis Bacon