An illustrated 2-part comparison diagram between 2 birds and their yelling amplitude. Their shriek is measured with a wave. A bird on the top has a low shriek amplitude, and its mouth is open a regular amount. A bird on the bottom has a very high shriek amplitude, and its mouth is open very wide, like a cartoon.
https://local.abtmtr.link/media/d9396a8ba11b0a97ae76680b72b67c00edbe35eb6462e5b3ae763520e1d50db8.png