Masons have several "tricks" up their sleeves that they will use in the course of doing work.
One of these tricks is pretty sneaky and rather clever. It's about insuring that they get paid for their work.
One of the most common jobs a mason is hired for is to build chimneys. Anyone who has ever worked in construction -as a contractor- probably has their own tales about not being paid by the homeowner, or the main contractor, if you work as a subcontractor. Here's a trick masons use to make sure they get paid when they build a chimney.
Just a method to ensure payment. But if you upset the mason while they're working, you might end up with this: