If you hear something from "the horse's mouth," you're hearing it firsthand, from the source. If you don't, you could be getting bad information, or as Edie Brickell puts it in this song, "hearing it from a horse's ass."
In a 2021 Songfacts interview with Brickell
, she told the story behind the song: "Years and years and years ago, I think I was 20 years old and we were still playing in the clubs, and one of the local newspapers said something about our band that wasn't true. After that article came out we were really affected by it because when you're so young, you're unaccustomed to being written about, and certainly when somebody gets it wrong, it felt so crushing, and it was mildly insulting.
We had a regular following, and a crowd of kids who were there to see us every show. And in between songs, in one of those impromptu moments, I said to our crowd, 'Hey, I know that they said this in the press, but it's not true, and if you don't hear it from the horse's mouth, you're hearing it from a horse's ass.' And we all fell out laughing."