They are sharp, really sharp!
Since the Stone Age, the blades that have been used as surgical tools, known as Obsidian blades are known to have one of the sharpest edges in nature. These blades are so very sharp that even as doing little harm to the tissue the individual cells could be cut in two halves by them. This is helpful in healing the incisions with less scarring and fast.
The mucus protects it from attacks:
The parrotfish are known for the amazing feature of sleeping inside a snot gurgle. To protect themselves from the attack of parasites, they trickle mucus from their mouths every night before going to sleep and around their body, they make a cocoon of this. Also, it has been observed that after waking up in the morning, they stuff the mucus in their mouth.