In "The Crucible," what did Parris see in the woods the previous night?

As "The Crucible" opens, Reverend Parris reveals that he saw his daughter, Betty, dancing in the woods the night before. Betty was accompanied by her cousin, Abigail, and Parris' black slave, Tituba. The dancing caused Betty to swoon.

The sight of his daughter dancing in the night and the subsequent illness that does not seem to have a natural cause spurs the action within "The Crucible." It transpires later in the act that the girls were casting spells in the woods with the hope of killing Goody Proctor. Thanks to this, Reverend Hale is summoned to investigate whether witchcraft is the cause of the strange illnesses affecting the town's children.