指桑骂槐 Point at the mulberry and curse the locust tree. To scold one person while really aiming at another.
旁敲侧击 Knock at the side, strike from the flank. To make a point indirectly instead of stating it.
话里有话 Words inside the words. A remark that carries a hidden meaning.
弦外之音 The sound beyond the string. Originally the lingering note of a piece of music. Today a meaning that is not said but can be understood.
含沙射影 Hold sand in the mouth and shoot at a shadow. From a legend about a water creature that spat sand at people’s shadows and made them ill. Today, to attack someone by innuendo.