When Sam is interviewing Consuela, she says the man had "bigote" which Sam translates as "beard" when it should've been "mustache". Although the killer that was being described didn't have any mustache so Consuela should've said "barba".
When Jim discovers Cal dead, the blood already appears congealed. It takes hours for this to happen, whereas Cal was discovered seconds after the incident and blood was still running down the front bonnet of the car. This is visible both during the opening scene and while Sam and Dean are watching the camcorder video at the police station.
When Paris Hilton's head had been cut off, There was so little blood and there wasn't any blood coming from her head or her body.
Dean says the buyer had verified the VIN (serial number) of the car, but they had to verify the engine number to make sure it had belonged to James Dean. The VIN, which is permanently attached to the car would identify the car, but the engine could have been changed, so the engine number is not a reliable indicator. Additionally, unlike the VIN, engine numbers are not recorded by states, so Sam would not have been able to use it to find the original owner as was shown.
When the Civil War buff is shot by "Lincoln", he is shot off-screen and supposedly killed in the exact manner of Lincoln; However, Lincoln was shot in the back of the head when he was assassinated and at close range by handgun, so there would be no castoff on the wall. Lincoln also died in a hotel room at the Petersen House across the street from his wounds a few days later, not immediately.
Dean tells Sam that James Dean's car "Little Bastard" is said to have disappeared in 1970 when it actually disappeared around 1960. The owner of the vehicle decided to have it shipped back home to California, the car was loaded into a boxcar in Florida. When the train arrived in L.A. , the boxcar door was still intact and sealed but the car was missing.
Even though it's used as a female name, the Spanish word for comfort/consolation is "consuelo" and keeps the "-o" ending. English speakers typically gender-convert the name to "Consuela" by mistake, as Dean does. Ms. Alvarez doesn't correct him, but she's probably used to everyone getting her name wrong anyway.