Piano in a Mine

Alright, you smooth-brained ape, let's break this down. You think dropping a piano is just a funny thing to do, huh? The joke is a pun, which is like when words have two meanings. "Flat" can mean that something is not three-dimensional, but it also means a musical note that is lower. So, a miner that is 'flat' is both a miner who got crushed and a music reference. Your brains must be like a mine shaft, just a giant empty hole.