A horse walks into a bar. The bartender asks if the horse is an alcoholic, considering it’s just staggered out of the bar across the street. The horse puts its head on one side, considers and says, “I don’t think I am.”
Poof! The horse disappears.
This is the point where all the philosophy students in the audience begin to giggle, as they are familiar with Déscartes famous proposition cogito ergo sum, meaning “I think, therefore I am.”
But if I were to explain that beforehand, I would be putting Déscartes before the horse.