Great aesthetics and clean puzzle design.
About the cards: I never succeeded with them nor was given a reward, but was cured anyway showing 2/3 ingredients in my inventory.
Bug?
Thanks for the kind words. The third inventory slot is just for the recipe / ingredients list, that you get, when you solve the card puzzle. It is not necessary to beat the game.
There should be hidden arrows, that might help to find the code, that you need to solve the card puzzle. But I have to admit, its really hard to notice :)