Today's comic is mostly an obscure conglomeration of in-joke, because sometimes you have to do that.
The passage in question is this one, from Macbeth:
ROSS
And Duncan's horses--a thing most strange and certain--
Beauteous and swift, the minions of their race,
Turn'd wild in nature, broke their stalls, flung out,
Contending 'gainst obedience, as they would make
War with mankind.
Old Man
'Tis said they eat each other.
ROSS
They did so, to the amazement of mine eyes
That look'd upon't.