"Farting Your Guts Out" joke

Bob and Martha have been married for 15 years. Every morning
for 15 years, Bob wakes up, farts loudly, rolls over onto his
back and gets up for work.
Every morning for 15 years, Martha says, "One of these days,
you're gonna fart your guts out!"
One Thanksgiving morning, Martha's preparing the turkey and
gets an idea. Before her husband gets up, she creeps upstairs
and places the turkey innards in his pajama bottoms, giggling
to herself.
Well, later that morning, Bob wakes up and goes through his
morning ritual. He screams as he goes running into the
bathroom. Martha laughs, but is concerned after noticing that
Bob has been in the bathroom for 3 hours.
She runs upstairs, and is about to knock on the door, when
Bob opens up, pale as a ghost. He says, "You were right. You
were right. I did fart my guts out, but by the grace of God
and these two fingers I got them back up there again."