This classic riddle asks: what can’t talk, but will reply when spoken to? At first it sounds like the answer must be a person, animal, or device. The trick is to think about something that repeats your words without actually understanding or speaking on its own.
The answer is an echo. An echo happens when sound waves bounce off a surface and return to your ears. If you call out in a canyon, tunnel, empty hall, or other reflective space, you may hear your own words come back moments later.
That is why an echo fits the clue perfectly: it cannot talk by itself, but when you speak to it, it seems to reply. Simple riddles like this are fun because the answer is familiar, yet the wording makes you think in a different way.
