By Kevin Young
Entertainment reporter, BBC News
South Park creators Matt Stone and Trey Parker have given a masterclass at the Edinburgh TV Festival, explaining the routine they follow to make their satirical animated comedy.
It's changed somewhat, but what's remained constant is that we write, direct and produce every single episode and do all the voices.
The show airs on Wednesday night in the US, and that means that the Thursday before that, we all sit down and say, 'What do you want to do the show about?'
Parker (l) and Stone (r) have written South Park since 1997
A week before the show airs, we don't even know what the show is going to be - which is cool because we can do exactly what is happening that week.
It's also really stressful. It keeps it exciting.
We'll have a big writers' retreat before every season and it will hopefully come up with a few big ideas. But it's still that Thursday that we sit down and say, 'What show will we do?'
More often than not, we don't have any ideas.
Sometimes we'll come up with, OK, alcoholism - what's our take on Alcoholics' Anonymous.
We'll start to figure out whose story it is, and come up with a scene and start a scene, because you've got to get something animated.
It's really more of a sculpting process.
Two scenes will get done on Thursday.
More often than not, we don't have any ideas
On Friday we'll come in and say what happens before that, or what happens after that, or is that the beginning?
On Saturday it builds up, and Sunday it builds up.
Then on Monday we're dying - oh my God, the show is on in two days and we don't have anything.
And then on Tuesday we're up all night and we always used to barely having it by Wednesday morning - and then it's on the air.
We can sit there on Monday night - literally this happens all the time - and we won't have an ending. We don't have the last four minutes of our show.
We'll figure it out, and then we can run to the booth, we do all the voices, send it up to animation - it all happens in one building.
We'll even write the pages knowing this is kind of it, this isn't it, and then we'll animate that, and we'll think, 'Oh, Cartman shouldn't say that, he should say this.'
And then I'll run to the booth and go 'nah nah nah nah nah' and come back over here, and I can see it animated in an hour.
The often controversial show is set in a small town in Colorado
We can write a scene and go, 'OK, now we've done this, let's put this whole scene not at Cartman's house but outside, in a Chinese restaurant.' And we can see that in an hour.
Meanwhile the storyboard department will draw a big board so I can take it and put the drawings where I want, so that tells the animators what to do.
We learned to write about three years into South Park. It's fun because we've still stuck with the show and we still do everything ourselves.
Now we go back and look at our early work - you know, 10 years ago.
It's pretty rough watching the first couple of seasons - like, 'Oh wow, we thought [at the time] that was good writing.'