Raindrops Keep Falling On My Head - S2-E1
Revealing mistake: When Derek Shepherd tells Meredith about his wife cheating you see Meredith Grey standing by her car and you can hear and see the rain all around the trailer, while Derek Shepherd is sitting on his porch under an overhang. Before Meredith sits down you can see rain hitting the hood of her car. When Meredith sits next to him she is completely dry. When she goes back to her car the camera does a close up and she is still completely dry even though her car is covered in rain drops and you can see the rain in the background. (00:37:10 - 00:39:40)
