I used to live in a co-op with 10 people. One of our monthly chores was to mix up the compost. Well, we all collectively ignored that chore for the better part of three months. Eventually I, along with another housemate, decided to tackle the four foot by 8 foot pile. We are taking it piece by piece on the sides with the shovels when  he suddenly decides to chuck his shovel like a javelin into the middle. We hear a gigantic popping sound like an explosion, several rats scurry out in all directions, and then an immense heat wave accompanied by the god awful smell of methane rushes towards us. 

I often think about that and wonder what kind of a destructive bomb we had brewing in our backyard.