After you click on the flag, don't start clicking, just read the instruction message and wait (7 seconds) for it to disappear. then click the left (normal) mouse button to see what happens. Next time press it for longer and see the difference.
This project is just to teach about how to use the "mouse up" event which is explicitly not present in scratch but could be used in this clever way (See inside). I just added a few lines, an interactive mouse image (to visually illustrate the click), remixed and then shared it. I hope you like my changes. Credits: 1. Thanks to nevit for the original project. 2. Mouse sprite taken from: https://openclipart.org/detail/24771/mouse-icon
