When the patient gives his pee sample to Dr Cox, the jar is half full. However, when JD has the sample in his hands later, the jar is completely full.
When Dr. Kelso is talking to Boone about losing a 19 year old patient, a view of the hospital appears. In the center window on the fourth floor you can see JD and many others standing. This is a printed window laminate which has been left when Elliot breaks up her engagement with Keith.
Both JD and Dr Cox pronounce "porphyria" with the accent on the third syllable: "por-fear-EE-uh". The correct pronunciation has the accent on the second syllable: "por-FEAR-ee-uh".