Spontaneous Human Combustion
I found an explanation about spontaneous human combustion which makes some sense.
Most deaths thought to be caused by spontaneous human combustion can be attributed to the "wick effect", whereby a person’s body fat acts like candle wax, causing a person to burn in an intensely hot but extremely well contained fireball. Strangely, all that is left in most cases is the lower part of the victims legs, which contain little fat, and their feet, which are usually found to be still wearing slippers. This would seem to explain how homes are sometimes left undamaged after a victim’s body has been burned to cinders along with their favorite armchair. However, whilst the "wick effect" explains the way in which a human body might burn it offers no explanation for the cause of the fire.