There are minor blood continuity differences between the Season 1 ending and the Season 2 opening of the aftermath of the crash when the demon possessed "Big Rig" driver broadsides the Impala. For instance, Dean has blood on the left side of his face especially around the left of his mouth that is gone in the opener of Season 2 Episode 1. Sam has more blood on his face, thicker and wider at the end of Season 1 than he does at the beginning of Season 2.
You don't shock a flat line.
When the doctor is talking to Sam about his brother's condition at the start, as the camera turns to Dean's body, where he is meant to be in a coma, you can see Jensen closing his eyes from where he was watching.
At around the 23 minute mark, Sam gets up after talking to Dean through the Ouija board, and says "Dad will know what to do." But his mouth barely moves, if at all.