Oddly enough, you could repeat this exercise today, strictly with the computer itself. How would you request from a friend a list of the files in a particular folder whose names end with a particular extension? If it's a GUI based system, you have to be just as explicit as with the glass of water. In fact, written instructions for performing computer operations are often page after page of pictures of dialogs with circles and arrows, plus paragraphs of text. And your dialogs don't look the same because you have a newer version of the OS.

And people get them wrong.

This didn't really strike me until I started using Linux, even though I had originally learned on command line based computers. The same instructions for Linux users are a few lines that you enter into a terminal. I've even noticed a trend towards documenting Windows operations via a series of commands entered into the DOS box.