In the 1939 classic film The Wizard of Oz, Scarecrow is mortally afraid of fire. Ironically, fire should have been the least of his concerns. Scarecrow’s costume, as well as one of the most iconic scenes of the movie, were fireproof because of asbestos.

Asbestos is a naturally-occurring mineral. It is composed of thin fibrous crystals, each of which contains millions of microscopic “fibrils.” Although asbestos has been used for thousands of years, it was in the late 19th century that it really took off. It is strong and pliable. It is excellent for absorbing sound. On top of that, it is highly fire-resistant. Because of these qualities, it was used in clothing, furniture, carpets, and many other everyday products.

Despite its many fine qualities, asbestos has a decidedly-negative side to it. Inhaling the microscopic fibrils is very bad for one’s health. Since the early 18th century, physicians have known that people who work with large amounts of asbestos were more prone to pulmonary fibrosis. It wasn’t until the 20th century that it was linked to a type of cancer known as Mesothelioma.

Today, most people know enough about the dangers of asbestos to stay well clear of it, but that certainly was not the case when Dorothy, Scarecrow, the Tin Woodsman, and the Cowardly Lion made their way through the poppy fields. The “snow” that miraculously appears was, in reality, asbestos.

The snow scene is not the only time the stars were exposed to the dangerous substance. Scarecrow’s entire costume was composed of it, as well. So was the broom that was wielded by the Wicked Witch of the West.