"I never told you this?" Harley blinks for a moment.

She can tell the story as she leads him to her Nexus apartment.

"Remember how I told you about how sometimes I laugh uncontrollably? That condition was caused by something called Joker Toxin. Contact with Joker Toxic causes uncontrollable spasms of laughter, leading to a painful death."

"I met Joker in Arkham. It was my first psychiatrist gig. And I..." Harley frowns. "I fell hard for him. He knew all the right things to say. How to create a connection that wasn't real."

"I even helped him to form a jail break. And he took me to where a bunch of Joker Toxin was stored in vats. He held a gun to my head and asked if I would die for him. Then he asked if I would live for him."

"I jumped... fell into the toxin. I died. I lived. I changed."

"The toxin changed me. It changed my skin tone. It changed my personality."