In a majority of cases, upon scientific investigation, alternative causes to supernatural phenomenon are found to be at fault, such as hoaxes, environmental effects, hallucinations or confirmation biases. Common symptoms of hauntings, like cold spots and creaking or knocking sounds, can be found in most homes regardless of suspected paranormal presences. People are more likely to experience a haunting when they are about to fall asleep, when waking, if they are intoxicated or sleep deprived. Carbon monoxide poisoning has been cited as a cause of suspected hauntings. If there is an expectation of a preternatural encounter, it is more likely that one will be perceived or reported.