system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do large piles of corn cobs spontaneously combust?

I was watching a tv show recently talking about using corn cobs to make things like football and bike helmets. They said that if corn cob piles weren't moved every so often they would begin to smolder from the inside and combust.
gpt
Large piles of any plant material is capable of spontaneously combusting given the right conditions. They produce and retain heat as they decay and are warmed by the sun or air. If they are dry enough and that heat high enough they will combust. 

This also happens with grain in silos, hay if the bales are too big, and even stacks of wood given the right conditions.