When a man inserts one end of a hamster tunnel into his asshole and the other end into the other male/females asshole. Then letting off a huge fart. Therefore sending his fart to the other person.
Toby: Jake do you wanna shuttle again?
Jake: Oh yeah, shuttle me, baby.
Toby: Good because I've been holding in this huge fart all day just for you ;)
Jake: I love shuttling with you Toby ;)
Like 'The Happening' It's the sudden realization that the shit your holding in is worse than you thought. Often when you feel you don't need to go and an immediate urge to shit heavily comes from nowhere
"Last week i was walking to work when i suddenly felt 'The Shittening' It was fucking insane!"