Related (first includes audio recordings):<p><i>The scary sound of Aztec skull whistles</i> (36 points, 1 month ago, 30 comments) <a href="https://news.ycombinator.com/item?id=42181466">https://news.ycombinator.com/item?id=42181466</a><p><i>Psychoacoustic and archeoacoustic nature of ancient Aztec skull whistles</i> (62 points, 30 days ago, 33 comments) <a href="https://news.ycombinator.com/item?id=42213125">https://news.ycombinator.com/item?id=42213125</a>