Kant's Beer

The following joke is usually told with different characters, but it works just as well as follows: Descartes, Hume and Kant walk into a bar. They each order a beer. A fly lands in their steins' suds. Descartes, calculates the volume of liquid oblivious to the fly. Hume, enraged by the presence of the fly orders another beer. Kant, picks up the fly and says, "Spit it out! Spit it out!" 

Kant not only intuitively sees the fly (empiricism), but does so according to his categories of understanding (rationalism). It's not a precise analogy, and too bad Kant is said to have advocated teetotalism, but it made me laugh nonetheless.