I'm starting "David Copperfield", and he mentions that he was born with a caul. That means part of the membranes which surround the infant in utero still covers the head after infant emerges. It happens only rather infrequently, so superstition attributed special abilities to the child,
and special values to the caul, which was preserved and valued. Here's a quote about it, from Internet:

A child born with a caul — a thin membrane covering the head — would probably be notorious in some way. This caul was supposed to be a preventive against shipwreck and drowning, and was accordingly purchased by sailors. This idea of the value of a caul was widespread, as would appear from numerous advertisements in the newspapers. One of these, which appeared in the London Times in 1835, was as follows

"A Child's Caul to be disposed of, a well-known preservative against drowning, &c., price 10 guineas." And a caul has been advertised for sale in a Liverpool paper in this year (1891).