Jared Padalecki was the reason for the clip at the end of the episode where Jensen lip syncs & air guitars "Eye Of The Tiger". He decided to miss his cue (of tapping on the car for Ackles to begin his act) to see what Jensen would do.
When Bobby replies to Sam in Japanese after Sam asks him if he reads Japanese, what Bobby says roughly translates into 'Since before you were born.'
At the end of this episode, an extra clip was added after the producer credits, titled "Supernatural presents: Jensen Ackles". The clip shows Jensen Ackles during what seems to be a take of one of the scenes in the episode, set to the song "Eye of the Tiger" by Survivor. However, the cut spans out beyond the scope of the original scene to an approximately 1 min long out-of-character performance with Ackles lip-synching to the lyrics, "performing" the song, complete with air guitar and the crew laughing in the background.
Jim Beaver, the actor playing Bobby, suggested to speak his line '"since before you were born" in Japanese, as he is fluent in the language.
Right before Sam explains ghost sickness to Dean, he offers his brother a box of donuts. Dean turns up his nose at them and tosses the unopened box into the car. Sam looks puzzled by this action, but in later episodes Sam and even Crowley state that if Dean turns down food, especially foods like cheeseburgers and pie, it is a sign that something is seriously wrong with him.