There are three quizzes for most video lessons.  Quizzes 2 and 3 are more challenging than Quiz 1.  The second and third quizzes are locked until the first quiz is successfully completed.  For each quiz, there are 2 green hearts.  If you answer a question incorrectly, you will loose a heart.  

If you answer 2 questions incorrectly, you will be bumped back to the video so you can watch it again to improve your comprehension.