Joker: Why? You need a reason? It’s probably the same reason I beat that puppy to death with a kitten last week. When the howling and meowing stops, and all you’re left with is a mess of fur and blood and brains—-well, you can’t beat that warm glowing feeling inside.
Batman: This has always been about us. Why did you do this to him?
Joker: Every time you and I play, I lose. I was getting a bit bored of always losing. I thought I’d try this on easy mode for a bit. And it was easy. It was as easy as beating a puppy to death with a kitten.
From – Injustice Gods Among Us #04