Are you serious? There was mercury in those mazes? LOL
Yep. That was Mercury. We used to buy those things at Thrifty Drug store for 50 cents. When the puzzle got easy, we'd break them apart and play with the mercury.
Those were the good old days. We used to sprinkle DDT on ant hills and pour our used oil into a hole in the back yard.
All my friends who died were killed in automobile accidents or drowned. Well, one guy died of meningitis and another had a heart attack during a basketball game. I think one of my friends was eaten by a shark (he walked out into the ocean and nobody ever saw him again). The shark probably died later from mercury poisoning.