mumble (/mutter) to oneself; think aloud ❍ 他不是～地走来走去，就是慌慌张张地跑出跑进，……(爱新觉罗·溥仪《我的前半生》170)When he was not walking up and down muttering to himself he was rushing in and out in a panic，…/我禁不住～： “走着瞧吧！ 我一定要赶上你们。”(吴运铎《把一切献给党》152) “You wait!” I muttered aloud. “I’ll catch up with you yet.”
喃喃自语nán nán zì yǔ
喃喃：小声唠叨。形容自己小声唠叨着什么。mutter to oneself, think aloud, mutter under one’s breath