Explain xkcd: It's 'cause you're dumb.
'Undeclared' is sometimes called "General Studies".
Here's a YouTube video of "I Am the Very Model of A Modern Major's General"  for those who need to get the tune.
Here's is Tom Lehrer's Elements.
And here is Supercalifragilisticexpialidocious from Mary Poppins.
In panel 4, Methyl acetate is the solvent used to remove stamps from their envelope.
In panel 8, underwater basket weaving is a commonly used metaphor for any college major that is easy or worthless.
In panel 25, supermoon and zodiac are terms invented not by astronomers, but rather by early astrologists.
In panel 26, agronomy is the science of using plants as food or fuel, while the unrelated agoraphobia is the fear of wide open spaces.
And Sophie's Choice is any dilemma where choosing one cherished person or thing over the other will result in the death or destruction of the other, derived from the theme of the novel, and has also been turned into a romantic drama film.
People have done renditions of this song. See 
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Panel 1's cueball is in the same pose as Rodin's "The Thinker"
Panel 4 background is the periodic table of elements.
Panel 5, Fowler's Toad emits a noxious secretion that irritates skin and mucous membranes (it was previously thought to cause warts)
Panel 6, Psychology = a serial killer with a chainsaw, Sociology = hobo; Social Psych = hobo serial killer with chainsaw.
Panel 15, LISP, Scheme, and other computer languages with an excess of parentheses.
Panel 16, biohazard symbol
Panel 19, bongos were played by Richard Feynman
Panel 27, fear of snakes, study of reptiles
Panel 28, a picture of a stomach, pun on "stomach" being slang for "tolerate"
Panel 30, words in all lowercase like e.e.cummings
-- 18.104.22.168 22:04, 7 December 2012
- Hobo serial killer with chainsaw? Social psych sounds awesome!
- 22.214.171.124 22:42, 22 October 2013 (UTC)
In panel 22 (History), what's the theme connecting the years 1935, 1969, and 1991?
Wwoods (talk) 15:40, 21 May 2013 (UTC)
This explanation is very small for that big comic. I am starting to add the transcript and after that I will do more investigations to that opera. This should be the key to explain all the panels.--Dgbrt (talk) 19:13, 21 May 2013 (UTC)
- The answer won't lie in the song, trust me. Pirates of Penzance is probably my favorite comic opera out there. Plus Randall gives that the lie in saying you can use the tune from the elements song (a well-known parody) or even Marry Poppins (similar tune, but not exactly the same). I think each panel is just a reference to the words, I don't think that Randall is actually involving The Pirates of Penzance in any way other than the tune. 126.96.36.199 20:53, 9 December 2013 (UTC)
Feynman was also known for being a ladies' man, so the two girls in panel 19 are significant IMHO.
--188.8.131.52 13:51, 25 December 2013 (UTC)
Needs explanation what does it mean to choose a major, and what major is in this context. Note every reader is from U.S.A.; different countries have different higher education systems. --JakubNarebski (talk) 10:56, 9 January 2014 (UTC)
- True that. 'Graduation' in Brazil means 'Undergraduation' in the US. 184.108.40.206 03:51, 1 February 2014 (UTC)
"Math's just physics unconstrained by precepts of reality" - that isn't a binary tree, its a bifurcation diagram from chaos theory. And, sorry, it has nothing to do with the Banach–Tarski paradox - that's just mindless name-dropping.
Davidbak (talk) 20:54, 10 February 2014 (UTC)
https://www.youtube.com/watch?v=pRexBMPeRToHalfhat (talk) 18:59, 3 April 2014 (UTC)
Panel 30: possibly iambic septameter220.127.116.11