the sound your backside makes when you have recently eaten something potent.
its a 2-syllable fart: the 1st part is a quiet, suppressed and discreet noise; the 2nd is ultra loud and represents a failure to contain the pressure of the rectum
"this week, i have been mostly eating bake beans, scotch eggs and drinking fizzy pop!".... gu-HONK!.... "pardon me :S"