A horse walks into a bar… and orders a beer.
As the bartender serves him, he looks at the horse and says “hey,
you look a little long in the face. Do you think you might be depressed?”
The horse ponders for a second, scratches his chin, and says “I don’t think I am” – and promptly disappears.
See, this is a joke about Rene Descartes’ famous statement,
“I think, therefore I am.” I could have mentioned this at the start of the joke, but that would be putting Descartes before the horse