נָ֥חָה שָׁקְטָ֖ה כָּל־הָאָ֑רֶץ פָּצְח֖וּ רִנָּֽה׃
全地得享安息，一片平靜；眾人都放聲歡呼。
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.