Move the mouse after clicking the green flag. This is an interesting project from 2004 because it shows that Scratch from that time had cloning and that the green arrow (flag) first did a broadcast to "setup" and then did a broadcast to "go". Press space to see some of the old 2004 code.
This was linked on a web page describing how to use Scratch dated Oct 2004 with several sample programs. The directory used to be found at http://llk.media.mit.edu/courses/software/scratch I modified the program as needed to allow it to work under Scratch 3.0 Please see the programs in this Studio: https://scratch.mit.edu/studios/30767325 Thanks GNOMEOTRON5000 for pointing out a copy error with changing hue by 10 to the new Change Color effect. (The default is 25 and I just used the current default).