Too subtle for me

A Horse walks into a bar....
A horse walks into a bar and orders a double whisky.

The bar mans says “you are in here pretty often, do you think you may be an alcoholic?

The horse replies “I don’t think I am"- and completely vanishes from existence.

See, the joke is about the philosopher Descartes, who said “I think, therefor I am”

But, to explain that part before the rest of the joke, would be putting Descartes before the horse.​