UPDATE: so now it doesn't reveal any squares anymore.

I suspected sth must be wrong with event handling, so I added the following lines to the code: myevents = pygame.event.get() if len(myevents) != 0: print(myevents)

(I put it into the main Game Loop, inside the "while True", just before "for event in pygame.event.get()"...)

The output that generates is this. Note that I clicked on a different square each time, so I don't know why the position doesn't keep changing:

[<Event(4-MouseMotion {'buttons': (0, 0, 0), 'rel': (229, 375), 'pos': (229, 375)})>, <Event(5-MouseButtonDown {'pos': (229, 375), 'button': 1})>, <Event(6-MouseButtonUp {'pos': (229, 375), 'button': 1})>, <Event(4-MouseMotion {'buttons': (0, 0, 0), 'rel': (-139, -326), 'pos': (90, 49)})>, <Event(5-MouseButtonDown {'pos': (90, 49), 'button': 1})>, <Event(6-MouseButtonUp {'pos': (90, 49), 'button': 1})>] [<Event(5-MouseButtonDown {'pos': (90, 49), 'button': 1})>] [<Event(6-MouseButtonUp {'pos': (90, 49), 'button': 1})>] [<Event(5-MouseButtonDown {'pos': (90, 49), 'button': 1})>] [<Event(6-MouseButtonUp {'pos': (90, 49), 'button': 1})>] [<Event(5-MouseButtonDown {'pos': (90, 49), 'button': 1})>]

(last line gets repeates as often as I keep clicking)

Any help would be very much appreciated. Thanks!