In the normal behaviour this exception is raised when you fail the memory test.
Did this exception raised before any mouse click in the window?
You are supposed to click the numbers in order, from 1 to 9 (even after they are hidden)
Yes, it was short in time to make a better "game over" screen, so I just raised an exception.
In the next version, I would like to make the game log every attempts, logging which number was reached, and in how much time. So that we can see the progress, and you can compare your ability to succeed the test with friends.