In an experiment, volunteers walked individually through a dark, abandoned theater. Half of the volunteers had been told that the theater was haunted and the other half that it was under renovation. The first half reported significantly more unusual experiences than the second did. The researchers concluded that reports of encounters with ghosts and other supernatural entities generally result from prior expectations of such experiences.
Which of the following, if true, would most seriously weaken the researchers' reasoning?
【选项】Each unusual experience reported by the volunteers had a cause that did not involve the supernatural.