After a period of three to four hours, the Foetus has absorbed and assimilated enough of the hosts' bodily nutrients to trigger its accelerated metabolism and rapid cell division. Once the creature has grown to the maximum size allowed by the thorasic cavity, it prepares itself for birth. This involves re-locating the head beneath the sternum and exerting tremendous pressure, secreting acidic compounds and breaking down the structural integrity of the bone and musculature imprisoning it. Whilst biting its way to freedom, the host is killed.