£20 For Meat?

[Rondy]

One day, a wife goes up to her husband and asks for twenty pounds to buy meat.
"Are you crazy?" says the husband, who pulls her over to a mirror. "Let me show you something? This twenty-pound note is mine. The one in the mirror is yours. Get it?" The wife nods. The next day, the husband returns home to find a freezer full of meat. Angry, he asks his wife about it. She pulls him over to the mirror and lifts up her skirt.
"See the one in the mirror? That's yours. But this one is the butcher's."