נָ֥חָה שָׁקְטָ֖ה כָּל־הָאָ֑רֶץ פָּצְח֖וּ רִנָּֽה׃
Вся земля в покое и тиха; они начинают петь.
Rashi
opened [their mouth] in song This is the song they recited, “All the land rested, became tranquil.”
Ibn Ezra
פצחו They break forth. The root פצח in Arabic means to speak poetically.