Beliefs about witchcraft varied. Some (but not all) people who believed in witches believed that they held nocturnal meetings called sabbats. At the sabbat they did wicked things like dancing naked, indulging in orgies and carrying out a parody of the Catholic mass. Witches were even supposed to kill babies and eat them!
Most people believed that witches could fly.
According to some authorities when a witch made a pact with the Devil he touched them and left a mark (which was not necessarily visible) on their body. The mark was insensitive to pain. One test for a witch was to prick their body with a blade. If they did not flinch or bleed when pricked in a certain place then it was evidence that they were a witch.
Many people believed that witches could affect the fertility of animals (very important when people relied on flocks and herds for their livelihood). They also believed that witches could make humans or animals ill or even kill them by magic.
Many people believed in 'swimming' witches. If a witch was thrown into water the water would 'reject' them and they would float. If they sank they were innocent. (Although they might accidentally drown!).
Women's History Magazine