I once toasted a bread roll with a very round upper surface. It was very hard, and I was curious about breaking it. So I whacked it with a spoon and instantly a

I once toasted a bread roll with a very round upper surface. It was very hard, and I was curious about breaking it. So I whacked it with a spoon and instantly all sound in the ear facing it was replaced by a ringing which faded slowly away over the next couple of minutes.