Paranormal activity describes unexplained activity in nature. Often, this includes the unexplained movement of objects, or unexplainable sensations. People experiencing (or claiming to experience) paranormal activity may see, smell, feel, or hear things that can't be explained by another source, and may be consistent with other aspects of their lives (e.g., someone who had recently lost a relative who was a smoker, may smell smoke reminiscent of that relative).
Critics of the study of the paranormal often cite this correlation as evidence that these occurrences are mentally created. Investigators (often known as "ghost hunters") have made definite observations, however, such as electromagnetic fluctuations, audio recordings, and images on still photos. As these events can be caused by other means, their value as evidence is debatable.