When fans opened the cover of Batman #663, they saw something comic fans usually don't -- a whole lot of words. While prose stories used to be a staple of comic books, they grew very rare by the Seventies. The use of prose, of course, means a lot more language inside the covers, including a very gruesome description of how victims of Joker toxin die.
One particularly terse passage delivers a rapid-fire soliloquy by the Joker in which he pinwheels from one thought to another, shuffling personalities until settling on a new one. Morrison's take on the Joker as a composite of multiple personalities corresponding to the past eras of the comics was fulfilled in this speech, because it was composed of past speeches, draw from the Joker's very first appearance up to the present. Most fans were able to spot some of the lines right away, enough to realize that the speech probably contained even more references than they spotted. Indeed, it's all references, and most from famous stories that have been reprinted, but two of the lines were from very old stories that are also very obscure.
When I was tracking down every possible clue to Batman, R.I.P., I was determined to track down each line of the speech, and I did. Now, here is the artwork in which each originally occurred. Enjoy!
They can't keep me here I know a way out.
You see I hold the winning card.
You're in my power Batman Ho Ho! I could pull off your mask
now -- and end your reign! I could even kill you but I won't!
Let him live! He's so amusing when he tries to match wits with me.
Take a look! We resemble each other!
And I'm looony, like a lightbulb-battered bug.
The Killing Joke
Aren't I just good enough to eat!
Stop... stop... stop me... if you've heard this one...
Batman #614 (Hush)