I didn't see any one ealse posting this so here:
If you have a combat knife in your hands go to any colider like sandbags or asomething, then sitdown and throw the knife up. It will multiply the knife into 2. I never seen others use it, but its still got to be fixed.
Basicaly what you get is once you throw it it will hit the colder and then dual it self. Thus only if the colider is high enof.
Works any map.