A joke about planes

So, Jack and Jill were just married, both age 20, and go to this funfair, which offers a plane ride for £20.
Jack: Please, can we go? I've always wanted to fly on a plane!
Jill: I'm sorry Jack. £20, is £20
20 years later, they go to the same funfair, have fun on the rides, until they come across the plane.
Jack: Please Jill! We're not that poor!
Jill: Jack, face it, £20, is £20.
And so when they go 15 years later, at the age of 55, Jack still want to go.
Jack: Jill, I want to go on the plane!
Jill: Jack, stop! £20, is £20!
And so, for the final time, they go to the fair when they are 65 years old.
Jack: Jill, I'm going to die soon, so I want to go on the plane!
Jill: I'm sorry Jack, but £20 is £20.
Just then, the pilot overhears them talking, and says:
Pilot: I'll tell you what. I'll give you a free ride, and do all the trick, and loops to make you sick, but you can't utter a sound. A single noise, and you'll have to pay.
Jack and Jill agree to this. They get on the plane, the pilot does all of his tricks. Jack doesn't make a sound.
When they get to the ground, the pilot says:
Pilot: That was amazing! What I did was enough to make anyone sick! You didn't say anything, or make a single noise!
Jack: Well, I almost did; when my wife had a heart attack and fell out of the plane...but I said to myself,
''Come on Jack, £20, is £20!''