Cox takes his flashlight out of his pocket after he gets on the elevator, when the camera is facing Kelso. In the next shot, Cox reaches to take the flashlight out of his pocket again. Then in the next shot, he already has it out and his hand is by his side.
When JD is caught dancing by Turk, then says "I'll just put on something that rocks," instead of something that rocks he puts on "A Beautiful Day" by U2.