Somewhere on FR yesterday, there was a post about how every so often in France, someone will unearth a 90-year-old WW1 mustard round and accidentally detonate it and die in the process.
Yes, I was in France last year, and saw a man with machine gun bullets, an American helmet, and a rusted German machine gun, all dug up that very day. He said he goes out often as a hobby to find artifacts with his metal detector. The amount of leftover war materials in Europe is astounding.
Another good reason to fight wars abroad rather than here.