18 Hz has been called the "Fear Frequency" following research suggesting that a tiger's roar contains strong infrasonic components at approximately this frequency. The theory is that the infrasonic element of the roar — too low for conscious hearing but powerfully felt in the body — may disorientate and temporarily paralyse prey in the moments before an attack.

This is not unique to tigers. Several large predators produce vocalisations with infrasonic components, and the physiological effects of low-frequency sound on the human body are well documented: increased heart rate, difficulty breathing, disorientation, and a primal sense of threat that bypasses rational thought entirely. At 18 Hz, the body responds before the mind can analyse what it's hearing.

Delivered here as a binaural beat with a 210 Hz carrier (left: 201 Hz, right: 219 Hz), the frequency is entirely safe at normal listening volumes. The predatory effects described above require extreme sound pressure levels that headphones cannot produce. As a binaural beat, 18 Hz sits in the beta range — associated with alert, active cognition rather than the visceral fear response triggered by high-volume infrasound.