What's up with that square under "water vapor"? Is it just a glitch, or is it some hidden message like in https://xkcd.com/1005/? Nick818 (talk)
I think it is a hidden message, it almost looks like a tiny graph.
It looks like a tiny version of the same graph, but flipped upright so that pressure increases as you go up. (Doing this in the main strip would ruin the "Under Pressure" joke. --Druid816 (talk) 05:19, 7 August 2015 (UTC)
I'd say it's the phase diagram Randall used as a template, see Wikipedia --184.108.40.206 05:28, 7 August 2015 (UTC)
According to this, it's a phase diagram of water from Wikipedia. 220.127.116.11 05:30, 7 August 2015 (UTC)