A proverb meaning that once you have spoken (or acted) you cannot take it back; words cannot be unspoken.
彼は軽率な発言をしてしまい、同僚から『吐いた唾は飲めぬ』と言われた。
He made a careless remark and was told by a colleague, 'You can't take back what you've said.'
会議での約束は慎重に。吐いた唾は飲めぬからね。
Be careful about promises in meetings — once you say them you can't take them back.