Open refrigerator. Say, "Hey, there's a big glass of grape juice that someone's covered with a piece of Saran wrap." Think that's kind of odd but not the strangest thing to happen. Remove glass from fridge. Remove Saran wrap. Drink liquid.
Race to sink. Say, "Hey, that's not grape juice; it's rinse water from purple paint brushes" while spitting liquid onto last night's dishes.
Return to fridge. Eye the glass half full of apple juice. Say, "Well, that doesn't look like a urine sample..."