Factual error: When Sam and Dean are showing Jo pictures of H. H. Holmes' victims, the last picture was a victim that was not his. The final black and white is Jack the Ripper's third victim, Elisabeth "Long Liz" Stride.
Factual error: When the doctor says that the dead man has a high lymphocyte percentage indicating a viral infection after she looks down the microscope: 1) What they show in the microscope looks nothing like what is actually visible down a light microscope (especially the supposed lymphocytes) and 2) Even if she could see what they showed, it wouldn't actually indicate that the infection was viral.
All Hell Breaks Loose: Part 1 - S2-E21
Factual error: Dean finds a body in the house that burned down. The arm has a metal watch still on the wrist with hardly any damage. It has some black soot on it but that's it.
Suggested correction: Your entry is based on opinion/theory only. It's possible for someone who died in a fire to have parts of their body to not be affected by the fire.
Simon Said - S2-E5
Factual error: The man gets hit hard enough by the bus to knock his shoe clear off, yet when we see his body about to be covered up, there's only a small amount of blood on his mouth. If you get hit by a bus hard enough to make your shoe fly off, then there should have been more damage.
