“To show you that beneath these faces, well, it’s just soft, tender stuff. Stuff you could just poke your finger through.” he tells Batman. “Beneath my grin, though, is just more grin! Ha ha! And beneath that face of yours is something snouted and fanged and lovely and that’s what this is about. Reminding you of the love we share, you and I.”
However the still masked faces are just replicas designed to trick them because Joker has no interest in who they really are. Batman points out that the Joker had chance infiltrate the Batcave but turned tail halfway and left his calling card. A flashback reveals Bruce Wayne visited the Joker in Arkham Asylum and returns his playing card but he doesn’t make the connection.
“He didn’t see me at all,” Batman explains. ” It was then that I knew — knew that he didn’t care who I was beneath the mask, and never would. Knew that he was incapable of even broaching the subject of Bruce Wayne. It would ruin his fun.”
In retaliation for tormenting them, Batman pretends to know the Joker’s real name. He begins to whisper it in his ear but the Joker pulls away and falls off a cliff.
The Joker has the last laugh though. Batman discovers they’ve been injected with a miniscule amount of a radioactive isotope known as Hahnium, which has the element symbol Ha.