When Greg is playing the video that Earl left at his house, the Mac video player that he is playing it in reads 00:00:00 throughout and there is no active pointer running through the time line at the bottom (as is standard)
Each scene where Rachel is informing her friends about her test are different, the first time she stands in front of her friend, and the second she is hugging her friend.
Because of infection risks, flowers would not be allowed into a cancer patient's room.
Rachel is mentioned to be Jewish, and in her home, she has a Menorah. Yet on the funeral scene, the people are wearing black, and her body has been cremated. Even in non-orthodox Jewish families, you are not required to wear black on funerals, and it is completely forbidden to cremate a dead body.
Incorrectly regarded as an error: A family can be Jewish and consider themselves Jewish without being religious. In such circumstances, following some Jewish rituals may still have significance and offer comfort for such a family. Thus, Rachel may be cremated and mourners may wear black and males might still wear yarmulkes.
In the ending credits under "Special Thanks To" the Children's Hospital of Pittsburgh is listed twice.