When J.D. asks Kelso when he got an earring, Kelso flashes back to his explanation to his wife that he wasn't cheating on her; the earring was his. He then proceeds to pierce his own ear, leaving it bloody. However, the whole time he is talking to his wife before this, he has a red, blood-like stain on his collar, probably from previous takes.
During the episode Dr. Kelso is seen wearing Dr. Cox's lab coat.
The clock on the wall behind JD and Dr. Cox jumps from 9:30 to 2:50 from the time Dr. Kelso enters the rich patient's room and when he leaves a few moments later.
During the scene where they're competing with wheelchairs, you can see the bar that extends under the chairs that enable the riders to remain tilted.
Around 9 minutes into the episode when Kelso is talking to J.D. and Dr. Cox, he's is wearing a lab coat with the name tag that reads Perry Cox MD instead of Dr. Bob Kelso MD