WWII-Era Exploding Chocolate Bar
From the website of the security Service, more commonly known as MI5, comes this spy gadget from World War II: an exploding chocolate bar.
This ordinary-looking bar of chocolate is really a German hand grenade. It's made of steel with a thin covering of real chocolate. When the piece of chocolate at the end is broken, a strip of canvas is pulled out. After seven seconds the bomb explodes.