Understanding vs. Knowledge

As written in dictionary.com, understanding is the mental process of a person who comprehends while knowledge is the acquaintance of facts, truths, or principles, as from study or investigation. Both understanding and knowledge are mental process a person makes. However, I believe there is a difference. For you to understand something, there must be a "click" in your mind. for example if you see a rose flower with thorns on the stem and someone tells you that thorn hurts, it is easy for something to click in your mind and you to see the sharpness to the thorn and understand that that thorn can hurt you. However, you do not know how much it could hurt you or what the degree of pain is. That comes from knowledge because the only way you can find out exactly how much it hurts is by experiencing it yourself.  Understanding comes from the mind while knowledge comes from an act. In other words you do not need knowledge to understand. You can understand something first and then choose whether you want to investigate it and become knowledgeable on the particular subject. Having knowledge is going beyond what a normal person would understand in a subject. Understanding and knowledge can work together or they can stand alone. Either way both are important.