So one person takes a really huge hit off the bong and holds the hit in. He then goes over to the other person, who is lying on the floor with their ass in the air, and blows the smoke into his ass. The second person then farts the smoke back into the first person's face who then proceeds to huff it hard. This requires an air-tight seal from lip-to-lip (lips to asshole). This technique is popular in prisons utilizing crystal meth, and both people involved get blazed as fuck.