Why is scraping against coral different from simple rock abrasion?

Coral is a living, sharp, microbial-covered animal skeleton.

The danger associated with coral contact stems from its biological nature, distinguishing it significantly from simple rock abrasion. Coral is classified as a living animal, specifically polyps, which secrete a rigid, sharp calcareous outer skeleton. This structure is often covered by living tissue but, upon contact, the underlying rigid skeleton tears the skin. Furthermore, the surface harbors a collection of viruses, bacteria, and slime. When contact occurs, this foreign material, including microbes and physical fragments, can lodge deep within the skin, leading to a high potential for serious, lingering infection, unlike the relatively sterile surface of many submerged rocks.