Dear Human,

Hi, Ruke here.

Have you ever heard an echo?

If you shout and hear your own voice shout back at you,

that was an echo.

An echo is not a person or even a thing. An echo is a reflection.

A reflection is what you see in a mirror or on the surface of water, or just about everywhere.

Everything you can see, like a color or a shadow or a shape, is a reflection of the light shining on it.

An echo is a reflection of sound. Almost everything is able to reflect sound.

Just like different people have different voices. Everything has it’s own different echo.

Mountains and canyons and buildings made of metal have big, loud echoes.

Most people are able hear a mountain‘s echo, but very few can hear a pebble‘s echo.

Animals like whales and dolphins and even some people are so good at hearing echoes they can tell where things are without needing to look at them.

Hearing echoes is like being able to shout, “Where is my blanket?” and hearing your blanket answer, “I’m over here.”

If you could find a blanket that way, you would be using echo location.

Echolocation is seeing with sound.

But you can’t really find a blanket that way.

Blankets and other fluffy things are one of the few things that don’t reflect sound.

Instead they sort of eat sound.

If you have ever covered your head with a pillow when someone was playing their music too loud, you know that soft things are quiet.

If you could see with sound, a blanket would be a quiet place. A blanket would be the one thing that didn’t answer when you called it. A blanket would be a dark place. The color black is what you see when a thing doesn’t reflect any light. Hearing a soft thing would be like seeing a black thing.

You can’t see anything without making some light,

and you can’t hear an echo without making some noise.

I have a light on my head but I live in a huge, dark ocean. I need to use echolocation if I want to see into the distance.

Here is how it works.

“EEEEP!!!”

I just made a noise. Imagine these three dots are three different smaller eeps. Echoes of the first eep that I made.

What could they be? My ears tell me more then that though. Imagine all these dots are different noises.

They sort of look like fish now.

It’s hard to describe my sound-sight to most humans. Sound can be a lot like light. It kind of shines on things. When I made that first noise. This is the image appeared in my head.

　Now I will make another noise. “EEEEP!”

Now the fish are in a different place!

Making a noise is like taking a picture. You have to make lots of noise to hear/see things moving.

“EEEEP!EEEEP!EEEEP!EEEEP!EEEEP!EEEEP!EEEEP!EEEEEEEEEEEEEEEEEEEE . . . . . .

Annoyed yet?

I thought so.

Echolocation does have some problems.

The pages of books are always blank when I try to sound-read.

I can’t make out pictures either.

You can probably guess why I normally just carry a glow fish lantern.

But hey, sometimes a world without sun really can be fun.

I’ll make a noise and you can connect the dots.

Print out these pictures and see what adventures are hiding in the dark!