Spontaneous human combustion refers to the death from a fire that originates without an external source of ignition and people believe that the fire starts inside the victim's body.  Many cases have been cited as SHC, but it's never been scientifically proven.  If this is a real phenomenon, why doesn't it happen more often?  

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Resources:

• Is spontaneous human combustion real? - HISTORY
• The Mystery of Spontaneous Human Combustion – Mystic Sciences
• Spontaneous Human Combustion - Historic Mysteries
• Spontaneous Human Combustion: Facts & Theories | Live Science
• Facts About the Not-So Spontaneous Human Combustion - Exemplore
• How Spontaneous Human Combustion Works | HowStuffWorks
• Cornelia Zangheri Bandi - Wikipedia
• Are Farts Flammable? Can They Explode? (firefighterinsider.com)
• 1951, July 1: Mary Reeser’s Fiery Death | Anomalies: the Strange & Unexplained (anomalyinfo.com)
• Non-Coding DNA | AncestryDNA® Learning Hub
• Super Powers Encyclopedia (mysticinvestigations.com)
• Pyrokinesis | PsiWiki | Fandom
• The unexplained death of Michael Faherty, Spontaneous Human Combustion – Strange Unexplained Mysteries (coolinterestingstuff.com)
• Death of Michael Faherty: Spontaneous Human Combustion Victim (anomalien.com)
• Is There A Paranormal Cause To Spontaneous Human Combustion? - Ask Mystic Investigations
• 1468~1503: Polonus Vortius’ Fiery Death | Anomalies: the Strange & Unexplained (anomalyinfo.com)
• 1938, August 27: Phyllis Newcombe’s Combustion | Anomalies: the Strange & Unexplained (anomalyinfo.com)
• John Irving Bentley’s spontaneous combustion (graphic) – Horror History .net