Quick heart refill question
Is it automatic when you lose a heart, or you can control it in some way?
You can control it. If you have lost all your hearts, it is up to you whether to use the refill (and get one extra opportunity to make a mistake without failing the lesson) or to risk finishing the lesson as you are. In the latter case, if you make the last mistake, the owl will cry and you will fail. The heart refill will remain for the future.