In the heat of passion, the person you are fucking puts their mouth over your asshole. At this point you rip a good fart into their mouth. Then, the person puts their mouth up to your mouth and blows your own fart into your mouth. Inhale deeply.
Man, I stank swapped the shit out of Todd's wife last night. She put her fat lips up to my asshole and I ripped a gnarly fart into her mouth. Then she blew my own fart into my mouth. It was great! STANK SWAP!