1 SFX: Knock! Knock! {the Charity Collector Guy is standing near the Head Death's receptionist's desk, arm raised}
2 Receptionist: CAN I HELP YOU?
2 Charity Collector Guy: I'm here from Taxes. I'm the auditor.
3 Receptionist: BUT, YOU'RE A MORTAL!
4 Charity Collector Guy: Flattery will get you nowhere.
4 Receptionist: ALL RIGHT, FINE. THE HEAD DEATH'S OFFICE IS RIGHT THROUGH THAT... WAIT. WHAT DID YOU KNOCK ON?

This strip went through a long and difficult development process.

I originally wrote the script as follows:

1 SFX: Knock! Knock!
2 Receptionist: CAN I HELP YOU?
2 Charity Collector Guy: I'm here from Taxes. I'm the auditor.
3 Receptionist: BUT, YOU'RE A MORTAL!
4 Charity Collector Guy: Flattery will get you nowhere.
4 Receptionist: ALSO, HOW DID YOU KNOCK?

In my mind this made perfect sense. The receptionist's office doesn't have a door - it's just a desk somewhere in the middle of the Infinite Featureless Plane of Death. The Charity Collector Guy's main schtick is that in the first panel of each strip he knocks on someone's door. The fact that he can knock on a door - even when there isn't a door there - is funny!

I assembled my set to take the photos for the strip. I placed the receptionist's desk and chair and her figure. And of course I placed the connecting door between her office and the Head Death's office, which we've seen there before. I took the photos. In the first panel, because the Charity Collector Guy is outside the receptionist's office, I left him out of the photo (even though there's no wall or door to be in the way). Again, this made perfect sense to me.

Then I assembled the strip, and added the dialogue:

Once I'd finished, I looked at it, and I realised that maybe the punchline might be slightly confusing to some people. She's asking how did he knock, but there's a door visible right there. It looks a little bit like he came in through that door (he didn't, but I can see how it looks that way), so asking how he knocked might seem a bit weird.

I showed some of my friends the completed strip and asked if they got the joke. They were all just confused. I thought, okay, clearly it just needs some explanation that the door that is visible in the strip is not the door that the Charity Collector Guy entered through (since he didn't enter through any door). So I modified the dialogue to try to make it clear that the visible door is the connecting door to the Head Death's inner office, not a door to the outside world that the Charity Collector Guy would have come through:

I showed my friends, and they were now even more confused. They didn't understand why the Head Death's office was relevant, or why the receptionist would bother mentioning it, and it seemed to contradict the obvious fact that the Charity Collector Guy had knocked on and come through the visible door, and why was she still surprised at how he knocked on the door, and ... just HUH??

I tried to explain how in my head this was all perfectly obvious, because the door that was visible in the strip was not the door that he knocked on and came through, because the door that he knocked on and came through did not exist. This just caused more head scratching among my friends, so I drew a diagram for them:

See, it's a perfectly normal office, with a receptionist's antechamber, and an internal connecting door leading to the Head Death's office. The only gotcha is that none of the walls exist, and the door between the receptionist's antechamber and the outside world does not exist. I was sure that this diagram would explain the joke successfully to my friends.

But they all just said, "What... What??? Now I'm even more confused. How can he knock on a door that doesn't exist?? ..."

And I said, "THAT'S THE JOKE!!!!"

And they added, "... When there's a door that does exist right there? Yeah.... maybe you need to rewrite this."

At this point I turned to my Patreon account and posted the problem strip for my patrons to discuss. There was a lively discussion between several patrons, with some good suggestions for how to make the joke more understandable and save the strip. I liked many of the suggestions, and in the end decided to combine those of Daniel and Heather, who suggested a reworded punchline and reshooting the first panel to make it obvious that the Charity Collector Guy was knocking on nothing (or rather, on the empty place where the front door should be). And you see the final result above.

So thanks to my patrons, who helped make this strip possible! (And if you're interested to be in on such comic workshop discussions - or just want to support my work in general - please consider pledging a bit over on Patreon.)