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)
Continuity mistake: Season 1 episode 2, Wendigo conflicts with this episode. Originally the wendigo information is printed on the left-hand side of the journal. On the right side is loads of symbols and text. Here the "same" page featuring the wendigo can be seen when Dean and Sam are searching for the asylum information but it's different.
Continuity mistake: As Sam is looking for the next victim in his visions, she walks by with her baby in a stroller. The baby is a completely different looking doll the first two times shown, but is blue-eyed Rosie when Sam approaches and interacts with her. (00:12:30)
Continuity mistake: When Sam gets the skeleton heads out of the back of the car, he brings the box in his arms long ways, but when the shot goes back to him it is turned the other way. (00:22:50)
Bloody Mary - S1-E5
Continuity mistake: When Jill's friend is saying how Jill died and mentions her eyes, she has her hands lowered in one shot but raised in the next. (00:16:11)
Continuity mistake: When Dean says he's going to talk to Amanda to get a grip on her mental state he has his head back on the seat and is looking straight ahead. When the shot changes he's now looking at Sam. (00:27:20)
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.