The low sonorous fart that starts off sounding like a burp but ends up 'fizzling out' at the end... can often be affected by following through and therefore should be attempted only when sat on the toilet.
"You may think this bally foolish of me Jeeves, old sport, but yesterday I risked a brough over at the Twamley's residence... Bally lucky I hadn't eaten the pea soup, what?"
"Indeed sir" replied the snooty butler.
From "Sniff That Jeeves" by F.U. Shithouse.