A shart attack is what occurs when multiple sharts take place. You shart
once, but figure that the chances of it happening again so soon are infinitesimal, so you fart again. And guess what, it's a shart. This, however, is only a double shart. A full blown shart attack is when the subject is stupid enough to do it more than twice in a row without repairing the situation (new underwear, shower, etc.).
He thought for sure that it couldn't happen three times in a row, but lo and behold, he was having a shart attack.