When Elliot and Carla are arguing the first time, Carla says "el barrio." When J.D. rewinds time and the scene replays, she says "*the* barrio," even though every other line (inlcuding J.D.'s sentence that he intended not to say) is identical to what it was the first time.
When Turk describes The Catch during the 1981 NFC Championship Game he states that there was no time left when there were actually 51 seconds left.
Just before the ton of bricks fall on J.D., he flinches in anticipation of them falling on him.
When Mrs. Tanner "escapes " from the hospital, you can see the tarp covered with dirt move as she gets up out of the hole.
In the first scene, after J.D. has rewound time, as the girls start arguing again the shadow of a crew member can been seen moving across behind them.
When Turk tells his patient he's going to take his fruit cup, he actually takes his patients Jell-O cup, you can see there is a fruit cup in the patient's tray as well.