A pollardy offer

I think I owe lots of people an apology. Yesterday’s blip was a spoof, an alternative fact, fake news. I saw the gaps in the wall, thought they looked like zips and made the whole thing up. Then I emailed the blip-link to my son because he’s a civil engineer with a taste for storytelling and I knew he’d have a laugh. But I got this reply:
I had a brief look at it this morning on my phone and couldn't really see the picture so spent all morning thinking about it. Then, when I got to lunch I saw it on a bigger screen and started composing a really serious email trying to get to grips with how it works. Just looked at the link in your blip and worked out that it was satire.
 
Oops. Sorry. If he didn’t realise why should anyone else?
 
Since you have no reason to believe me about anything ever again I won’t say a word about pollarding – there’s lots on the internet and some of it is true.