Bat

every flap is a call. the rock answers.

fly a bat through a cave by ear; tap to call, and the nearest rock's echo always answers first

A bat calls, then listens; the echo takes time set only by distance, since sound travels 343 metres a second there and back. Near rock is heard before far rock, building a picture from time. Sound here is slowed about 12x so order can be heard.

Concepts: sound, perception, biology.

An interactive you play with one thumb, on Wundr.