On a much less
pseudoscientific note, spontaneous combustion is a truly
verified, non-
controversial thing that happens to
inanimate objects. Spontaneous
combustion occurs when there is a combination of
flammable material, an
exothermic chemical reaction (such as
oxidation or
fermentation), and inadequate
venting of heat. This has been known to happen to piles of
leaves,
lumber,
hay,
oily rags, and even powder-free
latex gloves1.
Spontaneous combustion of hay is especially notable. Such combustion is actually encouraged by moisture. Moist hay set in the sun will heat rapidly and eventually ignite. The combustion will release hydrogen cyanide gas, which is extremely toxic, if the hay has been treated with preservatives.2
(1) See http://www.fda.gov/cdrh/glovepha.html
(2) Information from http://www.gov.on.ca/OMAFRA/english/livestock/dairy/facts/hayfires.htm .