The trick is in delivery with the SBD.
You realize you're having a slow but gradual pressure buildup like filling a tire. The tire in this case is also called a spare tire, the air is yer fart vapours. You can't escape to relieve the pressure. The problem is that if you wait too long or the gas builds up too fast, you'll have some embarrasing stomach noise that sounds like a fart but isn't the real thing! Anyway, the trick is to plant one cheek firmly on the seat as a sort of anchor (I usually choose my right one for this since i'm right handed, I must also be right-cheeked)
Now, the next skill is to ever so gently lift the other non-anchored cheek and pry it away from the anchored one thus causing a sort of controlled release of immense pressure and stink. Execute this perfectly and you will get away with da bomb and no one will know it was you - just look around like you're looking for the perpetrator like everyone else.
Screw it up and what you just attempted will sound like letting a big balloon go slowly by squeezing the top between two fingers - squuuuuuueeeeeeeeeeeeeeeeeeeeeeek!
boa
i'm doing one now ....