Some people believe it is unlucky for a black cat to cross their path, as they were once associated with witches and evil. For example, during the Salem witch trials, many of the witches were accused of interacting with cats carrying spirits. In folklore tales that reach back to medieval Europe, black cats are able to carry evil spirits and demons.
The idea that black cats bring bad luck or cause evil stretches back by hundreds of years. In medieval Europe, they were seen as so satanic that some people would burn bonfires to throw them on. These ideas continued into the early 17th century when Pilgrims first began arriving in America. Later in the century, during the Salem Witch Trials, several trials recorded the accused as having marks that indicated a cat had suckled on the witch. As cats were thought to carry demons and evil spirits, the accusers assumed they were causing the witch's supposedly evil behaviors.
In some countries, superstitions surrounding black cats continue. In Germany, a cat crossing a person's path from right to left is a sign of bad luck, but crossing in the opposite direction indicates prosperity is on the way. In contrast, people living in parts of Russia see black cats crossing their path as a sign that disease or death is on the way.