Why does a meme spread?

Mike asked for access to this. From the point of view of memetics, it's really interesting and extremely viral. Why? Because it's funny, portable, customizable (which gives the meme-spreader the sense that he is adding something), compact, direct (although it uses misdrection).
It allows the spreader to assume the illusion of a greater level of technical, information-sharing expertise than he really has. (Anybody can do this, but it looks complicated.) It concerns something that people care about. It makes a point. It uses familiar tropes. (I'm convinced that this is one of the keys to the viability and motility of a meme -- that it introduces new content using recognizable themes and tropes.) For a meme to spread, it must invite and permit the meme-spreader to look smart or clued-in, right? That's one reason you spread something is because it makes you look sharp. Another reason is that you think people need to know it.