A characteristic of the Drabatan species, who are amphibious, was a vocal pouch. To communicate in a less noisy and more straightforward secondary language compared to their main language, Drabatese, Drabatans used these pouches, modulating the pitch of the croaking sounds they produced by forcing air through them.
The reference book Star Wars: Rogue One: The Ultimate Visual Guide, authored by Pablo Hidalgo and published in 2016, initially brought vocal pouches to light.