Всякие фанатские вики ничего кроме фантастики не пишут, чем все это и является Shortly after the Chestburster erupts from the body of its host, it will flee due to its vulnerable state and attempts to find a secure location in which to molt its skin, where it then cocoons itself in a chrysalis made of a material similar to the Ovomorph's skin. The alien then grows inside until mature or disturbed. Inside, it experiences a dramatic growth spurt, growing from less than 1 foot (30 cm), to over 7 feet (2.2m), reaching an adult size in a matter of hours.

Либо прощаемся с законом сохранения массы, либо возвращаемся к вдыханию 120 кубов воздуха (хотя тут ещё термояд понадобится).