All Hell Breaks Loose: Part 1 - S2-E21
Continuity mistake: Before the Roadhouse fire, Ash and Dean are talking on the phone. Ash looks at his watch, on his left hand, it says 8:10, and has a black dial/face. As Dean and Bobby go through the rubble, Dean identifies Ash by his watch. Still on his left hand, it is now upside down, evident by the crown of the watch (used to move the hands of the watch) which previously facing his hand, is now facing his elbow. Also, the dial/face of the watch is now silver instead of black. This is a different watch, and was inadvertently put on the burnt arm upside down.
Continuity mistake: When they first bring the girl to the house with the storm and lay her on the bead the there candles next to her. First the tallest one blows out then the middle one blow out then the shot changes and the middle candle blows out again.
Continuity mistake: As Dave is leaning over the edge of the air boat with Rose behind him, he pulls a chunk of metal out of the water and places it on the edge of the boat on his left side. When he gets up from his lying position moments later, the metal is gone. Moments later again, with an overhead shot of the boat, we see what appears to be that piece of metal positioned at what would have been his right side, not his left. This is also where we see him step over the seat (twice!) in subsequent camera angles. (00:30:00)