system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When a bomb from World War II gets discovered and needs to be defused, why did it take so long to find it, especially if it is in a populated area?
gpt
Typically these bombs fell from the sky and hit the ground very hard, ending up buried underground (if they didn't explode). Something got built over the top of them, with no one knowing there was a bomb under there. They're discovered when someone starts digging, for example to make a foundation for a new building, or to put in a new sewer line or subway.