Part of the joke is the inherent logical fallacy of a cart being put before a horse.
The other part is the horrible, horrible pun.
Pianist goblin needs a supporting role at the very least!
I'm sorry, but jokes have to stand up to rigorous logical, historical, and psychological analysis before they can be submitted to the general public. For example, did you know that Descartes did not, in fact, die trampling, but rather of pneumonia? Clearly, you need to fact check your jokes more rigorously for such errors.