The "Watseka Wonder" refers to a series of events in the 1870s involving a young girl named Mary Roff from Watseka, Illinois. She reportedly exhibited signs of possession, including speaking in different voices and displaying unusual behaviors. This phenomenon attracted attention from both the public and spiritualists, leading to investigations into her condition. The case gained further notoriety when Dr. E. W. Stevens, a local physician, claimed that Mary was possessed by the spirit of a deceased girl named Lena Roff, her cousin. The events surrounding the Watseka Wonder contributed to discussions about spiritualism and the nature of consciousness during that era.