system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What are Cankersores and why do they hurt so badly?
gpt
canker sores are ulcers - sores where the surface tissue over an area has disintegrated, leaving an open wound that heals slowly.

It hurts because its an open wound that heals slowly in a part of the body that moves a huge amount and is unavoidably exposed to food and drinks, which irritates them and makes it hurt more.