I played and completed the game twice on expert mode without skipping a mini-puzzle or using a single hint on either playthrough, yet I did not get the final achievement, i.e., "Perfect Game" - Complete the whole game without using a hint. I thought perhaps I may have accidentally hit the hint button on the first playthrough, but I know without a doubt that I did not unintentionally hit the hint button on the 2nd playthrough, and I never saw a "hint" come up in either playthrough. I'm a bit pissed about that as it affects my overall Steam score for "perfect games."