Hello This is an extract feom Rain Fall by Barry Eisler. "You lay your own booby traps for the enemy - that was one of our specialties, tit for tat - but there are only twelve of you and you can't win that kind of war of attrition no matter how much more you bleed them than they bleed you. You take more losses, and the frustration - the rage, the strangling, muscle-bunching rage - just builds and builds." Would you like to give me the meaning of "muscle-bunching" in this case? Thanks.