At the beginning when J.D. and Turk are in bed Turk pulls the covers off of J.D. to reveal that he is completely dressed for work including his jacket. Right before the covers are pulled off of J.D. there is a camera close-up on him, and you can clearly see that he is not wearing a shirt or a jacket because his shoulders and collar bone are exposed.
When Dr. Kelso taps JD on his shoulder they are in front of a nurses station. The next shot shows Kelso giving a chart to JD and they are then in front of a patients bed.
Just before the Janitor squirts J.D. with water for the second time, J.D. is holding a patient's chart. In the close-up shot of J.D.'s crotch, both his hands are visible and he isn't holding anything.
When Dr. Kelso is waiting on the elevator him and Dr. Cox have a conversation and Kelso gets on and JD is in the background. The next scene shows Dr. Kelso tapping JD on the shoulder even though he just left that floor.
When JD borrows a pair of scrubs bottoms from Chet, Chet says "Don't stain em'" but the actors lips don't move.
When the main characters are "drifting" through the hallways you can see the trolley that Carla stands on as well as the cable pulling it.