A hidden force may be quietly shaping how you feel—and you’d never even know it. Infrasound, an ultra-low-frequency vibration below the range of human hearing, is everywhere from traffic to old buildings. In a small experiment, people exposed to it became more irritable, less engaged, and even showed higher levels of the stress hormone cortisol—despite having no idea it was present. The findings suggest our bodies can “sense” these vibrations without conscious awareness, potentially explaining eerie sensations in places like basements or supposedly haunted buildings.