Catwoman had stolen some kind of powerful device, something the Joker had been after. Which mean she didn't want him to have it. Which would have been fine, if Batman hadn't been after her as well. Which caused her to play cat and mouse. She was likely going to give him the device... if he caught her first after some fun. And kept her from stealing it back.
"Catwoman. I know that you have the device that Joker wanted. I need you to give it back to me." He said as he closed the gap between then.
She answered back to him, "Come and catch me, then you 'might' get it."
As he narrowed the distance even more, he leaped towards her. A little too much force from Batman, a stumble by Catwoman. This cause a chain of events, which ended with the device being activated. A glow of strange green light covered the two of them.
Feeling tingly, Catwoman got untangled from Batman, as she decided to...