In obstetrics, a caul is a portion of the amniotic sac which clings to an infant as it is being born. As a result, the child is born either entirely or partially still inside the amniotic sac, which often forms a veil over the infant's face. Historically, cauls were the subject of many superstitions; someone who is born with a caul is known as a caulbearer. Statistically, about one in 1,000 babies is born with a caul, and this number is often lower in developed nations due to routine interventions in the labor and delivery process.

In Europe, many people believed that a child born with a caul would be protected from drowning as long as the caul was preserved. Cauls were especially prized in fishing communities, as you might imagine. Other superstitions about cauls included the idea that caulbearers were born to rule or lead, or that they had supernatural powers over water. A caulbearer might, for example, make an excellent dowser, since he or she was supposedly in tune with water.

In some parts of Eastern Europe, people believed that an infant born with a caul was doomed to be a vampire later in life or after death. Some people destroyed cauls at birth to prevent this fate, and in other instances the caul was dried and ground into a powder which was fed to the child at a certain age, in the theory that this prevented vampirism.

Being born with a caul is not usually dangerous. The infant continues to receive oxygen and nutrition through the umbilical cord, and the caul can quickly be cleared away from the infant's nose and mouth so that he or she can breathe. In regions where people have superstitious beliefs about the caul, a midwife may take special measures to preserve it.

To preserve a caul, the caul is allowed to dry out entirely and then it is stored on acid free paper or cardstock. The caul may be wrapped in plastic or tissue paper to prevent degradation; examples of cauls over 60 years old can be seen in the hands of their owners in some parts of the world. By tradition, a caulbearer's special status was usually only retained if his or her caul was kept.

Due to the superstitions surrounding cauls, some people historically sold cauls or artifacts which they claimed were cauls. Advertisements offering these rare treasures for sale can be seen in some publications as late as the 1800s. Typically, the caul was purchased as a protection from drowning.