The play referenced in Chapter 75 refers to the webcomic Ow, My Sanity!.
The relevant paragraph of Chapter 75, for convenience of comparison and search:
"Oh," said the third-year girl, "I was thinking of that really romantic one where there's this very nice, sweet boy who makes a Floo call, only he mispronounces his destination and stumbles out into this room full of Dark Wizards who are performing a forbidden ritual that should've stayed forever lost to time, and they're sacrificing seven victims in order to unseal this ancient horror which is supposed to grant someone a wish if it's freed, so of course the boy's presence interrupts the ritual, and as the horror is eating all the Dark Wizards and everyone is dying the boy's last thought is that he wishes he could've had a girlfriend, and the next thing you know the boy is lying in the lap of this beautiful woman whose eyes are burning with a dreadful light, only she doesn't understand anything about being human so the boy always has to stop her eating people. This is just like that play, only you're the boy and Harry Potter is the girl!"
When I read that passage I would have bet a non-negligible amount of money that the work referenced was an anime or manga. Good thing I didn't.
edit: bloody hell is that webcomic terrible
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: