twist/turn the knife (in the wound)
idiom
        informal      
      
                                
                                
              
          
                                                      : to say or do things that cause more pain to someone who is already suffering                                      
              
                             
Any more cuts in government aid to these poor people will be twisting the knife in the wound.
                         
                
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  Merriam-Webster unabridged




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