As they drew nearer, however, his face shone through the gloom, hairless, snakelike, with slits for nostrils and gleaming red eyes whose pupils were vertical.
It rose, seemingly endlessly, and came to rest across Voldemort’s shoulders: its neck the thickness of a man’s thigh; its eyes, with their vertical slits for pupils, unblinking.
Voldemort was flying like smoke on the wind, without broomstick or thestral to hold him, his snake-like face gleaming out of the blackness, his white fingers raising his wand again — Hagrid let out a bellow of fear and steered the motorbike into a vertical dive.
"The Elder Wand," he said, and drew a straight vertical line upon the parchment.
Ron was pointing upward, toward the top of the hill on which they had appeared, where a most strange-looking house rose vertically against the sky, a great black cylinder with a ghostly moon hanging behind it in the afternoon sky.
Above what Harry assumed was the title of the story (being unable to read runes, he could not be sure), there was a picture of what looked like a triangular eye, its pupil crossed with a vertical line.
The Resurrection Stone had cracked down the vertical line representing the Elder Wand.
There are no more uses of "vertical" in the book.
Show samples from other sources
The architect used long vertical lines to pull the eye upward.
On a small ladder, a good-looking sandy-haired boy is painting a vertical sign that will say: "Doc’s."
Arthur Laurents and Stephen Sondheim -- Westside Story