Thanks you all for the useful feedback and comments. I didn't have time to fix collision detection which is not accurate enough. Sounds have been our greatest problem and not only because we just edited a bit our own voices, but also because our pygame.mixer.pre_ init settings seem to cause some errors. The key-pressing request between levels was made to make the player see what he has to look for. Would you believe us if we said we spelt "wawes" and not "waves" intentionally? Of course not and you are right.