The mistake is one of continuity in "Supernatural" Season Two, Disc Three, Episode Ten: "Hunted." It is early in the episode when Sam is at the roadhouse drinking a beer, the scene cuts and Ash steals a sip from Sam's abandoned beer. There is visibly more beer than when Sam set the glass down. It is a split second cut so no character would have time to add more. I say I'd like a magic beer glass that refills itself.