So basically it means to show that you really mean what you say by actually doing something or giving money rather than just talking about it for example the government talks about helping disabled people but doesn't put its money where its mouth is. To leave a bad taste in your mouth can be used to describe food, an experience which kind of makes you feel bad afterwards leaves a bad taste  in your mouth. Another one is watch your tongue watch your tongue or watch your mouth and that means be careful what you're saying around here because people are listening so watch your mouth don't say anything you shouldn't say watch your mouth um another one is by word of mouth word of mouth by word of Mouth