When a jet of liquid hits a vertical surface at 90 degrees, some of it will rebound.

Seagulls prefer not to swoop down if there's a risk of them hitting a hard vertical surface.

Horizontal flat lock panels are basically identical to flat seam roofing applied on a vertical surface.

Imagine the vertical surface of a wall lit by sunlight at an angle of about 45 degrees above the wall.

Sometimes, the wrigglers are spit onto a vertical surface rather than a pit.