Our toddler playing with a remnant of cold-war era explosives testing at Los Alamos.
A dent block, or "flinstone film" as we call it, was used to verify that a detonation fully propagated along some length or across some gap. Ten lbs of steel was far cheaper than fancier diagnostics. This block, not only dented, was bent probably 1/4" out of flat on the back side, 2.5" from the front. Explosives are really strong, kids...
There's piles of these blocks around LA. This one was in our garage when we moved in a few years ago.