Code Yellow is a pre-programmed trigger phrase used to control Jack by Frank Fontaine. Rather than triggering direct action, as the "Would You Kindly" trigger phrase did, this one triggers autonomic processes, specifically directing the subject's heart to stop beating. This doesn't happen immediately; as Fontaine notes, "The heart's a stubborn muscle, but it ain't that stubborn." The result is a series of periodic spasms that reduce Jack's maximum health, weakening him greatly over time. Fontaine uses this phrase in an attempt to eliminate Jack upon discovering that Dr. Tenenbaum had disabled the "Would you kindly" trigger.