Sometimes when the stork makes his deliveries, he forgets to take the packaging away with him, as this rare and fascinating footage demonstrates. The video, which was uploaded to Facebook by Jasmine Perez, shows a baby being freed from its amniotic sac, after being born still encased in the membranous pouch.

The amniotic sac is a bag of fluid that develops inside a pregnant woman’s womb, within which the unborn fetus sits as it grows. Made of two membranes, known as the amnion and the chorion, the sac and the liquid it contains serve to cushion and hydrate the developing baby, while also helping to maintain a constant temperature within the womb.

Normally the amniotic sac ruptures as a woman goes into labor, causing her water to break as the fluid rushes out, although in rare cases – fewer than one in every 80,000 births – this fails to occur, causing the baby to be born inside the sac, or "en caul" as it is known. When this happens, doctors or midwives have to slice open the membrane, allowing the baby to slide out, as can be seen in the video.

In other cases, part of the sac remains attached to the baby’s head and face, normally as a result of becoming caught around its ears. This is not thought to represent any danger to the newborn, although it is important to be very careful removing the caul, so as not to harm the baby.