Superstitions of Rural Life

Finding blood in milk or cows producing no milk at all would often result from poor hygiene or disease, but folk typically footed the blame at the work of a witch, using spells to steal milk’s goodness and make it impossible to churn into butter. The standard countercharm was for a farmer to plunge a red-hot poker into a churn.

Milk sours in thundery weather. To counter this, many farmers placed thunderstones on their windowsills. These were pieces of flint or fossil that farmers found in fields. Many believed these fell from the sky. Others perceived them as the remnants of ancient elf battle-axes. Whatever their origin, they contained the power that farmers needed to protect against all kinds of menacing witchcraft.

https://merl.reading.ac.uk/blog/2020/10/superstitious-countryside/