Spontaneous human combustion describes cases of a living human body being burnt without an apparent external source of ignition.
Many scientists regard it as a myth while other theories suggest that the fire is sparked when methane -- a flammable gas produced when plants decompose -- builds up in the intestines and is ignited by enzymes (proteins in the body that act as catalysts to induce and speed up chemical reactions).
Another theory is that the fire begins as a result of a build-up of static electricity inside the body or from an external geomagnetic force exerted on the body.
There have been about 200,000 reported cases dating back 350 years but not all have been thoroughly investigated.
The first written account came from the Danish anatomist Thomas Bartholin in 1663, who described how a woman in Paris "went up in ashes and smoke" while sleeping. The straw mattress on which she slept was said to be unmarked by the fire.