I really love xkcd. There's something encouraging about a webcomic focused on math and computer science that is nonetheless so funny and accessible that tens of millions of people read it every month. And every now and then it errs strongly on the obscure side, as exemplified by this recent comic that sent me off researching Paul Erdos in order to get the joke.
I learned that Paul Erdos was an extremely eccentric Hungarian mathematician who holds the distinction of authoring more papers than anyone else. And apparantly I'm not the only one, as "Paul Erdos" was Google's #1 hot trend last Thursday, when comic was published.