In tight spaces, a crowd behaves like water in a pipe: the more people, the higher the pressure. At the same time, entropy — a measure of chaos — increases, and a single push triggers a compression wave that, like gravitational waves, travels instantly through the crowd, knocking people off their feet. Previously, crowd movement was modeled as an ideal gas, ignoring physical contact. Now scientists account for compressive forces: at a density of more than 6 people per square meter, the lungs can't expand, and a person suffocates while standing upright. Such analysis helps architects design safer spaces. Surprisingly, a silent crowd is often more dangerous than a screaming one — silence hinders awareness of the threat until it's too late.