Jim Beaver's character (Bobby Singer) was only supposed to make a one-time appearance.
Originally Jensen Ackles auditioned for the role of Sam Winchester. When Jared Padalecki came in and read for Sam a slight recasting was done. Producers called Jensen and asked if he'd rather use his charm for Dean, saying he was the Han Solo character of the duo and what kid didn't grow up wanting to be Han Solo? Jensen accepted. It became known that he was previously interested in that role, because Dean was funny.
Jared Padalecki (Sam Winchester) dislocated his shoulder while wrestling with Osric Chau (Kevin Tran). The writers were then forced to make up a story as to why Sam was wearing a sling in the beginning of Season 10.
The original concept for Supernatural had a reporter going to investigate the urban legends and writing about them in his column instead of having the Dean and Sam concept.
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