A horse goes Into a bar, and orders a pint…
The bartender says “You know, you’re in here a lot. Do you think you might have an alcohol problem?”
The horse says “I don’t think I am…” and promptly vanishes from existence.
This was a joke about the famous line from philosophy - “I think, therefore I am.”
But if I had explained that at the beginning, it would have been putting Descartes before the horse.