He had shaved the wool from a piece of sheepskin, soaked, stretched, and dried it, and then fitted it over one end of the drumlike thing he had made, and tacked and bound it in a little groove at the edge.

He put the skin on damp so he could stretch it tight.

Then he punched a tiny hole in the middle, and pulled through it, down inside the drum, a sheepskin thong rolled in resin, with a knot big enough to hold it, and not tear the head.

Then he took it under his arm and we slipped across the orchard below the Station, and went into the hollow and tried it.
It worked! I almost fell dead with the first frightful sound.

It just bellowed and roared.