Carbon monoxide
Carbon monoxide can accidentally form when there is too little air to burn all the fuel into carbon dioxide. Such a situation may happen if the oven shutters are closed too early or if a mobile cooker is used in a small tent with no ventilation (Ventilation is fresh air coming in and smoke going out). Many people have died from carbon monoxide poisoning. Low-level carbon monoxide poisoning can cause feelings of paranoia and hallucinations, and has been determined to be a major cause of "haunted" houses. Higher levels of carbon monoxide can cause flu-like symptoms, headaches, and death. Small amounts of it are found in coal gas, a fuel produced by heating coal without any air.