A horse walks into a bar; the bartender asks, "Hello, do you want a beer?" The horse responds, "I think not," and promptly disappears.

Now, admittedly, this joke only makes sense if you are familiar with the French Enlightenment philosopher, Rene Descartes, who famously said, "I think, therefore I am." The horse thought not, and therefore wasn't...

But if I had explained that first, I would have been putting Descartes before da horse!