Here’s how explain xkcd works.
1) We post the cartoon on Monday, Wednesday and Fridays with our attempt to explain what is going on in the cartoon.
2) You comment on the cartoon and explanation and tell us what we have missed.
3) Others vote up or down your comment to help us pick out the best explanation.
xkcd is funny as hell (which is an odd saying; I imagine hell isn’t all that funny which makes this a pretty low hurdle, or so one might think) but can be quite obscure if you aren’t “in” on the topic of a particular cartoon.
h/t to J
My favourite xkcd of all time (useful as well as funny)…
http://xkcd.com/552/