The Mayan civilisation built large stepped pyramids. If you stand close to the base of such a pyramid and clap, the stepped feature reflects the clap back to you but changes the sound so that the echo sounds like a particular bird - the Quetzal. In those days (and even today) the Quetzal was considered a creature of great religious significance. Did the Mayan engineers know what they were doing? 1300 years later we can hear exactly what they heard. This podcast starts with four claps, listen very carefully to the chirp-like echo after each clap. This is followed by four chirps from a real Quetzal. They sound very similar don't they? Go to http://www.ocasa.org/MayanPyramid.htm for details.