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)
17 Seconds - S2-E26
Revealing mistake: When Burke and Alex find out that the heart donor patient is dead, and rush to revive him, in one shot of the donor's face you clearly see him blinking his eyelids. (00:13:35)
Revealing mistake: When Alex is talking to Rebecca Pope at the end of the episode, we hear Alex say "Now I know more about you than my friends." Watch Rebecca's left eye on the right if the screen when she says, "That's pathetic." Someone did a bad job of editing the CGI and we see a phantom eye over her left eyebrow.
Revealing mistake: When Ray is panicking over being in the rig with his dead partner, Stan, and turns to look at Meredith, you can see Stan's eyelashes flutter as he blinks. (00:36:37)