In making his point about the importance of carbon dioxide in the air that we breathe, Jonathan Miller came close to killing himself. As a demonstration, he re-breathed his own exhaled breath, but via a machine that removed the carbon dioxide from it. The body depends on the increasing concentration of CO2 in stale air, rather than the decreasing concentration of oxygen, to trigger the panic reflex to breathe more deeply or to do something else to escape the suffocating environment. On camera, he stopped breathing and passed out, and had to be hastily revived by the film crew giving him an oxygen mask.