On February 20, 1725, one of the strangest criminal cases in history happened in Rheims, France. On the morning in question, Jean Millet awakened in the inn he owned and operated with his wife. Surveying the establishment, he found a pile of ashes and a few internal organs in the kitchen. It turned out these were the remains of Jean’s wife, Nicole.

During a time when modern science was in its relative infancy, the scene was particularly perplexing to investigators. There was little left of Nicole, which would indicate an extremely hot fire, but little else in the kitchen had been burned. The bizarre situation began to look especially bad for Jean when it was rumored that he was cheating on his alcoholic wife with one of the maids at the inn.

Jean was charged with murder and later convicted and sent to prison.

But Jean appealed his case, and during his second trial he called a young surgeon named Nicholas Le Cat to testify on his behalf. Le Cat argued on the stand that there was no way a person could have started a fire that would have consumed the body so quickly and without causing major damage to the rest of the room.

Mrs. Millet, therefore, must have been the victim of spontaneous combustion.

That’s right, Jean Millet used the spontaneous combustion defense and actually won! In the centuries that have followed, this defense has never again been used at a murder trial. But there have been hundreds of other cases of spontaneous combustion throughout the world. These cases are rarely witnessed and usually involve someone finding a person’s remains in a pile of ashes with little fire damage done to the surrounding area. As creepy and supernatural as spontaneous combustion may sound, scientists think that there is a logical explanation for most cases—the “wick effect.”

This phenomenon takes place when the clothing of a burn victim soaks up the heated fat and acts like a wick, leading to an almost complete incineration of the body. Investigators have shown that in many of these cases the victims were smokers who fell asleep with a lit cigarette, which is what Le Cat believed happened in Nicole Millet’s case. This surely sounds logical, but not every case of spontaneous combustion has involved smokers. So that leaves us with many unsolved cases of spontaneous combustion.

Luckily, cases of spontaneous combustion are so rare you probably don’t have anything to worry about—unless you are a smoker, in which case this is just another good reason to quit.