system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why does hay spontaneously combust when it gets wet?
gpt
Hay is made from freshly-cut plant matter. When plant matter decays in a moist environment, bacteria and other microbial life thrive. Organisms generate heat as a natural byproduct of just being alive. The hay insulates the heat, so the hay cannot cool quickly enough. When the temperature reaches about 130ºF, the moisture and the microbial life undergo chemical reactions that release even more heat. Hay has a remarkably low ignition point of a little over 200ºF. For comparison, paper ignites at about 450ºF.