Throughout history, people have attributed warts to contact with things like sea foam, boiled egg water, and, of course, toads. Fortunately, we now know that warts are not caused by toads, but are actually caused by human papillomaviruses, or HPVs. So, how exactly do HPVs lead to warts? And what should you do if you get one? Cella Wright explores the science of these bumpy skin growths. Lesson by Cella Wright, directed by Anton Bogaty.