The act of passing gas from both one's mouth and anus simultaneously, usually caused by unexpectedly sneezing while trying to hold in a fart. Due to the great stress placed on the body while sneezing, the accompanying fart may be much louder and violent than a regular fart and often causes a small amount of anal pain.
This can be especially embarrassing in public places if the sound of the sneeze does not cover the sound of the fart.
On rare occasions, you may be unfortunate enough to encounter the 'twin-ender with sauce'. This occurs when the fart is accompanied by the expulsion of faecal matter (commonly known as a shart.)
Bill : "aaa... aaA... AAA-CHOOOFRRRRRRRRTT"
Bob : "Dude, wicked twin-ender!"
Bill : "...oh God, I think I ripped something."