The torso reflex (also known as the gasp reflex or inhalation response) is a physiological reaction – an involuntarily gasp – that happens when a person suddenly enters cold water. The reflexive sucking in of air is a way for the body to rapidly increase oxygen intake into the lungs as a means of increasing survival.
Some reported drowning victims don't die as a result of poor swimming skills or the effects of hypothermia, but from the torso reflex. Occasionally the torso reflex causes victims to inhale water. A person can also die from cardiac arrest brought on by sudden entry into cold water.