Spontaneous human combustion refers to the disputed phenomenon in which a person allegedly catches fire without an external ignition source. Reports of incidents circulated widely in the 19th century, and Charles Dickens incorporated such a death into Bleak House in 1853, defending its plausibility against critics. Modern forensic science rejects the idea, attributing such cases to overlooked ignition sources combined with the wick effect, a process in which subcutaneous fat liquefies and is absorbed by clothing or surrounding material, sustaining a slow, contained burn. This explains why victims often appear largely consumed while nearby objects remain untouched, and why extremities such as feet, which contain less fat, may survive intact. Even so, a 2010 Irish coroner’s ruling in the case of Michael Faherty controversially listed spontaneous combustion as the cause of death. Forensic pathologist Roger Byard states, “it’s deeply improbable, nigh impossible, that spontaneous combustion is the valid explanation for any of the alleged cases,” pointing out that “[i]t’s never been witnessed,” and if it were a phenomenon, “you’d be down at Walmart and suddenly the little old lady beside you, pushing a trolley would explode” (Leffer, Lauren. “Can humans spontaneously combust? The baffling cases explained.” Popular Science, 3 Jun. 2025).

Ernest applies these scientific explanations to account for both of the novel’s seemingly impossible deaths. Edward Huxley’s body, found melted in the vault, exemplifies the wick effect: His shins are burned through, and his feet are detached but unscorched. Ernest deduces that pistachios, classified under transport codes as flammable solids due to their oil content and capacity for self-heating when moisture is introduced, provided the ignition. The second death involves white phosphorus, a substance that ignites on contact with air at room temperature and was historically used in incendiary munitions and military flashbang grenades. Tobias Cuthbert weaponizes it by lacing sunscreen with phosphorus extracted from grenades, producing a chemical reaction that emits both light and heat and kills Bryce Fredericks through skin absorption and ignition.