matter of prefrence and to do knife hits you use a stove and ge tthe knives really red hot and either drop a lil ball of weed on to the knives or you pick it up with them....don't smash them together until your ready to start inhaling smoke cuz once you smash those fukers together is when it starts billowing up smoke like a chimney....also have like a one liter bottle (just cut the bottom part off)...in order to do this the easiest way hold 1 knife in each hand and hold the bottle with your teeth....