Indeed, they looked less like plants than thick, black, giant slugs, protruding vertically out of the soil.
Her head swayed this way and that, watching him out of those vertical pupils, her fangs bared… He flew higher.
Mesmerized, Harry looked up, high above him, and saw the eyes of the black dragon, with vertical pupils like a cat’s, bulging with either fear or rage, he couldn’t tell which…… It was making a horrible noise, a yowling, screeching scream.
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