i can do it too......you have to close your mouth and throat (where if you try to breathe out even with your mouth open nothing will escape) and keep it closed and give like a really fast and hard exhale but not opening your mouth your throat will hurt a lil bit (or just may feel like pressure depends on how receptive to pain you are...) then you just open your mouth and barely blow out....i can do it hours after i've been around smoke.....and it's possible because smoke stays in your lungs long after you quit smoking (not days or anything but quite a few hours)