Save butter knives and kitchen knives for only clearing buildings! These are extremely effective in tight quarters with their one shot kills. Don't waste them unnecessarily! Keep only one of each in your main inventory with the rest in a bag or pack. This is very important since if there is more than one butter knife (or kitchen knife) it will not switch to the second butter knife automatically, and you will have to play the inventory transfer game to drop the knife with the zero status. Whenever possible keep the butter knife equipped since they degrade the fastest (minimize carried weight). As soon as the butter knife breaks, the player will instantly switch to the kitchen knife, which is a lifesaver when facing multiple zombies in tight quarters (bathrooms). After five or so hits with the butter knife, check its status in your inventory (when safe) to see if its status is zero. If so, drop it, and equip another directly from your bag or pack (can be done in just a few seconds). Don't keep on using the kitchen knife if you still have butter knives--it's just for back-up. Keep one "outdoors" weapon (frying pan, rolling pin, baseball bat, etc.) in your main inventory in case you quickly blow through both the butter knife and kitchen knife, and don't have time to go into the inventory (it will automatically switch). Make sure this is one you are comfortable using indoors (I like the frying pan--golf clubs suck indoors). I have been playing sandbox with the zombie numbers at insane, which is why the above method was developed (out of necessity). There is just not enough time and too many zombies to knock the zombies down, then finish them off before other zombies are on top of you. Of course, this works just fine on settings lower than insane.
