Bart, who has decided to divorce his parents, enters a building in which numerous law offices are held. There is a sign next to the elevator showing the company names and floors. The names are all puns, like: "Luvum & Burnham, family law" and so on—all pretty straight forward gags. However, the last one Bart points to, says:
HACKEY, JOKE & DUNNIT I don't get it.
Edit: The 1 G-hit for this takes you to a German-language forum where one poster has apparently posed the same question and another explained it but, ja, it's all in German: 
Quote:
 Ein Whodunnit ist (wie du sicher weisst) ein Krimi (who did it), deshalb versteh ich die anderen Namen als brutale Toetungsmoeglichkeiten: 
hackey = hacken
Joke = choke = erdrosseln
Don't have a cow, man! [1]
—Elke 
 
[1] For best results, this should be read out loud in a thick German accent (—Hydra).