Have you ever wondered what a blood platelet actually does? Find out as the Once Upon a Time... series tackles biology.

Although antibodies mainly protect against bacteria, viruses, and other foreign substances, sometimes they can also attack your own blood cells! But this cartoon explains why you don't have to worry too much about that happening.

When the young platelets in this cartoon decide to have some fun and create a sort of "platelet pyramid" out of themselves, their older friend warns them that they could be causing a blood clot!

Watch the blood platelets in action in this fun cartoon. Moral of the story? Always listen to your mother.

The platelets vanquish the bacteria in the final installment of this animated series on blood. Who knew that a simple cut could be so epic?