A little old lady is walking down the street

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"....