and odd noises are typically present in any home, especially older ones, and "such noises can easily be mistaken for the sound of footsteps by those inclined to imagine the presence of a deceased tenant in their home." A sensed-presence effect, the feeling that there is someone else present in a room, is known to happen when people experience monotony, darkness, cold, hunger, fatigue, fear, and sleep deprivation. Skeptical investigator Joe Nickell writes that in most cases he investigated, he found plausible explanations for haunting phenomena, such as physical illusions, waking dreams, and the effects of memory. According to Nickell, the power of suggestion along with confirmation bias plays a large role in perceived hauntings. He states that as a house, inn, or other place becomes thought of as haunted, more and more ghostly encounters are reported and that when people expect paranormal events, they tend to notice conditions that would confirm their expectations. Many places deemed to be haunted are purposefully left in a decrepit condition, with wall paper peeling off, old carpeting, and antique decor. Toxicologist Albert Donnay believes that chronic exposure to substances such as carbon monoxide, pesticide, and formaldehyde can lead to hallucinations of the type associated with haunted houses. Donnay speculates on the connection between the prevalence of gas lamps, during the Victorian era and start of the twentieth century, as well as stories of ghost sightings and hauntings, describing it as the "Haunted House Syndrome". Donnay says that carbon monoxide poisoning has been linked to haunted houses since at least the 1920s. He cites a 1921 journal article about a family who claimed hauntings because they suffered headaches, auditory hallucinations, fatigue, melancholy, and other symptoms which are also associated with carbon monoxide poisoning. In a modern example, Carrie Poppy, a writer and co-host of the podcast Oh No, Ross and Carrie!, was convinced she was living in a haunted house. She felt she was being watched by a demon, experienced pressure on her chest and auditory hallucinations. Someone on a forum of skeptical paranormal investigators suggested she look into carbon monoxide poisoning. When the gas company arrived, unsafe levels of carbon monoxide were found. Michael Persinger, an American-Canadian professor of psychology, suggested that perceived apparitions, cold spots, and ghostly touches are perceptual anomalies caused by variations in naturally occurring or man-made magnetic fields. However, a study by psychologist Chris French that attempted to replicate