Looking for a story about people who live in a giant's teeth

I'm trying to identify a story where people got eaten by a giant, and somehow managed to avoid being swallowed and live in the giant's teeth.

I believe that the main character was a man, who was caught by people who were already living in the teeth. I think that they had hollowed out the teeth?

I remember one scene where the main character regrets not being able to catch an old man, who got swallowed.

I think it was in a collection of stories. The cover might have been red? I read it around 2011, I think, although I think it was older than that.