A Chestburster is the next stage after a Facehugger. After being facehugged within time a Chestburster will emerge. It's host will painfully die because of major blood loss and the lungs being busted and also the ribcage. Killing the host before it emerges can stop it because a live body is heated which keeps it alive and also the Chestburster. If the host is dead the body will go cold and the Chestburster will die.