What's the "een" in Halloween?
See spontaneous generation.
the hypothetical process by which living organisms develop from nonliving matter; also, the archaic theory that utilizes this process to explain the origin of life. Pieces of cheese and bread wrapped in rags and left in a dark corner, for example, were thus thought to produce mice, according to this theory, because after several weeks, there were mice in the rags. Many believed in spontaneous generation because it explained such occurrences as the appearance of maggots on decaying meat.