After finishing Guards! Guards!, I discovered that not only had I skipped a book, I had skipped a short story as well.
While "Troll Bridge" is not Pratchett's first short story, it was the first of them set in Discworld.
It was a story that got me to buy a book that was a collection of short stories called After the King. And at the time it was like methadone getting me to the next Pratchett book.
Pratchett uses a little bit of magic in having the horse talk (it having formerly belonged to a wizard), and acts as Cohen's... not conscience, but more like the voice of least resistance. It would certainly have been a great horse for Rincewind to have.
Pratchett also continues the naming convention of the trolls to be rocks. I was laughing a bit at a troll named Mica though.
Appearing in this story:
Cohen the Barbarian