Provenance - S1-E19
Other mistake: In the scene where Sam, Dean and Sarah go to compare the painting to the earlier photo of it, Dean, noticing the changed position of the razor, says, "Jared, check it out." He is speaking to the character Sam. The actor's name is Jared. [Confirmed in cast interviews].
Audio problem: When Dean puts the cassette in the car stereo he reads 'Metallica' off it, yet AC/DC plays. [In the original version Metallica was played, but AC/DC was used in newer versions due to copyright issues.]
Bloody Mary - S1-E5
Continuity mistake: When the real Jill is being Killed the blood lines from her eyes go from smeared to "clean" lines instantly. (00:14:20)
Visible crew/equipment: Before The End of the episode, Sam and Dean are thanked by the sheriff's daughter and her son. When Sam and the mother are left alone, his microphone wire is visible when he stretches. (00:41:00)
Factual error: At the beginning of the episode it is stated that we are in the month of April - yet in the orchard there are ladders, fallen apples and baskets filled with fresh fruit everywhere, as if it were harvest time. The god is declared to grant fertility and not climate change, so the harvest decoration seems definitely out of season.
Revealing mistake: When Sam pulls Angela out of the bathtub and on to the floor, you can see the panty line from the nude colored panties she's wearing to keep the show PG13.
Continuity mistake: In the scene where the passengers board the plane at the beginning, the aircraft is a Boeing 737, noticeable by the crew jumpseats located by the entrance door. But the first scene you see where the aircraft is in flight, the aircraft changes to a Widebody Airbus, possibly an A310, noticeable by the different style of winglets that Airbus uses compared to that of Boeing. (00:02:15)
The Benders - S1-E15
Continuity mistake: When the Deputy handcuffs Dean to the car door handle, he uses a small radio/cell antenna from the car to pick his handcuff lock (attached to his wrist), just as the bad guys walk toward the car. When the bad guys get to the car Dean is gone and so are the handcuffs (including the cuff that was attached to the door handle). Dean did not have time to pick both handcuff locks.
Bloody Mary - S1-E5
Continuity mistake: In the scene where Jill is looking at her 'Bloody Mary' reflection, the lines of blood coming from her eyes go down and straight over her mouth (because she hasn't smeared them like the real Jill has). But as she begins to talk, the lines switch from being over her mouth to off to either side of her mouth and back multiple times. (00:14:20)
Hell House - S1-E17
Visible crew/equipment: Right before they light the house on fire, the shot cuts the to the hell hound guys and a cameraman is running up to them on the right. Not just an arm - his whole body, including the camera.
Continuity mistake: When Sam and Dean break into Lori's dorm, Sam notices (and the camera pans towards) an open window. The camera then cuts to Dean. When the camera cuts back to Sam the window is closed. We watch Sam open the window and climb through it.
Factual error: At the beginning of this episode, it says "one week later", then it shows Dean and Sam go to the victim's apartment. The blood is still bright red. After a week it would be darker.
Continuity mistake: In the very first scene with Lori and Rich kissing in Rich's car, Lori's seatbelt is shown to be over her arm close to her shoulder. The camera cuts to Rich and back and the seatbelt is now behind her arm and lower without her having moved at all.
Bloody Mary - S1-E5
Continuity mistake: When Sam is looking at the mirrors with night vision, we see him pause and say to Dean "Look at this." The camera then cuts to an extreme closeup of the camcorder screen and the image on the screen is different to what was on there before. (00:18:15)
Continuity mistake: At the start as we see the victim on the plane, we see a blonde woman sat in the middle seat 2 rows in front of his row. When he gets up to stretch his legs, this blonde woman has now changed to a Chinese one. (00:02:45)
Audio problem: The pilot asks Amanda how she is at the start. When Amanda replies the audio doesn't match her mouth. (00:02:10)
Continuity mistake: Dean circles the newspaper article on Sophia Carlton. When he hands it to Sam the circle is different. (00:03:20)
Continuity mistake: When the first victim stands up to stretch his legs, he grabs the seat in front of him and his arm is bent. When the shot changes his arm is now straight and he's holding the middle of the seat not the edge. (00:03:00)
Answer: Angel blades come from angels. It's their angelic magic that makes it special. Therefore, an archangel blade is made magical with the powers of an archangel. They couldn't have just created one or used one, as none of them are archangels.