Lady with $20.00 bills in garbage bag

A little old lady is walking down the street, dragging two plastic garbage bags with her, one in each hand. There's a hole in one of the bags, and every once in a while a $20 bill is flying out of it onto the pavement. Noticing this, a policeman stops her...."Ma'am, there are $20 bills falling out of that bag..." "Damn!" says the little old lady....."I'd better go back and see if I can still find some. Thanks for the warning!" "Well, now, not so fast," says the cop. "How did you get all that money?" " Did you steal it?" "Oh, no", says the little old lady. "You see, my back yard backs up to the parking lot of the football stadium. Each time there's a game, a lot of fans come and pee in the bushes, right into my flower beds!" "So, I go and stand behind the bushes with a big hedge clipper, and each time someone sticks his little thingie through the bushes, I say: $20 or off it comes!" "Hey, not a bad idea!" laughs the cop. "OK, good luck! By the way, what's in the other bag?" "Well", says the little old lady, "not all of them pay up"....