Corrected entry: When we first see The Scar of the hand on Dean's shoulder, its on his left shoulder. Throughout the rest of the show it's on his right shoulder.
Corrected entry: In the scene when John is talking to Mr. D in the diner, Mr. D tells John to "say hello to your old man for me." It is later revealed in season 8 that John's father left them when he was young. This is a mistake, unless Mr. D is referring to John's grandfather (unlikely). (00:04:40)
Correction: It's never mentioned what happened to John's mother. She could have remarried, and so it could be John's stepfather being referred to.
A stepfather is the only explanation that would keep the canon consistent (other than Mr. D referring to John's maternal grandfather, or even to John's mom given that The Winchesters shows her to have been a rather tough mechanic), but out of universe, the writers almost certainly just forgot about this line.
Corrected entry: When the killer murders the dog she writes on the wall in the dog's blood "too late", but they said she was locked away her entire life so she wouldn't have known how to write or read. (00:16:35)
Correction: Why not? People have been known to learn to read and write on their own.
Death Takes a Holiday - S4-E15
Corrected entry: Sam and Dean Astro-Project out of their bodies so that they can see and save a Reaper. They are out of their bodies, walking down a street as ghosts, but their breath is visible due to the cold weather outside. Ghosts have no body to generate warm or hot breath.
Correction: First, it's astral projection, not Astro-projection. Second, ghosts are not proven to exist, as such we don't know their physical or spiritual characteristics well enough to judge if the have body heat or not. Some reports of supposed ghost phenomenon have reported cold spots in rooms, some as hot spots in rooms. Seemingly contradictory, but just more evidence that we don't really know what they are supposed to be like in characteristics.
Correction: The Scar is on his left shoulder throughout the series until it is removed. It is not shown on the right unless you're mistakingly seeing it as the right shoulder in the mirror shot at the beginning of the episode.
sthrnsass