The first of five clues. Each one below gives a little more away.
I only ever repeat, and never once agree.
In myth I was a nymph, cursed to have no words of my own.
Bats and submarines both trust me completely.
I need a hard surface and about seventeen metres of distance to exist.
Shout into a canyon and you will hear me.
Echo
Sound covers 343 metres a second, and your ear needs a tenth of a second to tell two sounds apart. Hence seventeen metres, and not one less.
Ovid gave the phenomenon a name and a story: a nymph punished with the loss of her own words, left only able to repeat. The physics is simple and the biology is not. Lazzaro Spallanzani showed in the 1790s that blinded bats fly perfectly and deafened ones cannot, a result so unwelcome that it was dismissed for a century until ultrasound could be detected. Submarine sonar arrived in the First World War and worked on the same principle. The opposite extreme is an anechoic chamber, where the absence of reflection is so complete that most people find it unbearable within minutes.
Reading five clues at once is not the game. In the real thing they arrive one at a time and every wrong guess costs an hour. Play mystery #30 · today's mystery · the vault
Previous: mystery #29. Next: mystery #31. Or try #50, #51, #52, #53, #54, #55.