Hot Knives are a way of combusting cannabis resin.

First get a glass milk bottle and drop a cold knife into it handle down. Holding the bottle by its neck rotate it in a conical motion so that the heavy end of the knife continually impacts the circumference of the inside-bottom of the bottle. After some time raise the knife and drop it back into the bottle. This should push the base out fairly cleanly leaving you with a useless milk bottle, but with an entirely useful glass cone.

Next get two butter or similar knives and heat the ends of them in a flame on cooker until they start to glow cherry-red. While they are getting real hot get a lump of resin, as big as you think you'll be able to take. Hold the top of the bottle in your mouth. Using one of the hot knives, touch the end against the lump of hash and pick it up then use the other hot knife to compress the lump between the two red hot knives. At this point the lump will combust with a sudden and large release of hot smoke which one inhales with the bottle.

Upon feeling the lungs burning moderately to terribly badly, cough like you just inhaled vapourized sulphuric acid, crumple to the floor and roll around hacking like you're about to die. Finally get really paranoid about the irrepairable damage you've just done to  your lungs. Grow hair and listen to rawk.