The corners of his mouth were wine-stained and his expression did not change, but Robert Jordan watched his eyes narrow, as a cat’s pupils close to vertical slits in a strong light.
Then another staff came behind them blasting with its klaxon and flicking its lights off and on, and each time the lights shone Andres saw the troops, steel-helmeted, their rifles vertical, their machine guns pointed up against the dark sky, etched sharp against the night that they dropped into when the light flicked off.
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