Chapter 12, The Silent Valley, how is sound made?

From the text:

"No one realizes how much trouble we go through to make them," she complained. "Why, at one time this shop was crowded and busy from morning to night." "But how do you invent a sound?" Milo inquired. "Oh, that's very easy," she said. "First you must decide exactly what the sound looks like, for each sound has its own exact shape and size. Then you make some of them here in the shop, and grind each one three times into an invisible powder, and throw a little of each into the air every time you need it."