they apply a freeze treatment to a skin blister.

This happened to a friend of mine. She had an unusual problem on her foot that she wasn't sure what it was. The doctor decided that it was a wart so she applied liquid nitrogen to it to freeze the wart.

It hurt so much that my friend screamed in pain. The doctor yelled at her for screaming because a wart is dead skin and it shouldn't hurt.

Later on, my friend saw her family doctor, and it turned out to just be a blister caused by toes rubbing together too often.

That's a pretty simple diagnosis to get wrong.