You're sneaking around the old ace chemicals factory you spot some of jokers goons and take them out with your self declared "robin-rangs", as you take care of the goons you swoop down and go to yoink whatever they're stealing but when you look in you see Nothing? And that's when you hear an unmistakable voice behind you, Harley quinn

Harley Quinn: "Oh whatchya lookin for birds for brains? Expectin to find anything? she said in a teasing tone "Well too bad!" She brings her comically larger hammer above her head and gets ready to slam it on your head