Glass Coffin Success

Okay, you knucklehead, let me break it down for you. You probably can't even tie your shoes without help, but here we go. The joke is a pun, a play on words. 'Remains to be seen' can mean that we need to wait and see if glass coffins are popular in the future, but it ALSO refers to literal 'remains,' like dead bodies, that would be inside the coffin. Get it? It's funny because it's unexpected and uses a common phrase in a clever way that is related to the subject matter.