A lesson in bacteria

Cook pasta. Leave the pasta in its water in case you want to make soup, scooping out pasta as needed for other dishes. Leave pasta in its water in the pot on the stove (physically, but gas off), figuring it can't go bad in a day, right? Discover 18 hours later that no, it does have an off smell already.

This happened years ago with a rice and lentil thing, actually: left it moist on the stove, it smelled bad a day later. In both cases, it's a gas stove with a vigorous pilot light, so there actually is some heat input even when 'off'. Also in both cases, the food was warm, whether from the pilot light or from vigorous biological activity or both. I suppose I could experiment, with the pot moved somewhere else. (And not the top of the fridge.)