When Castiel rebuffs Sam and Dean's questions about the angel who attacked Cas, Dean says, "Stop, alright. Too many angels, Cas. I don't know who's on first and what's on second." Dean is quoting the famous comedy routine "Who's on First?" by Abbott and Costello.
At 08.21, when the boys first enter the morgue, the doctor/forensic pathologist in the room is Robert Singer, the director of this and several other Supernatural episodes.
First appearance of Balthazar
At one point Balthazar says "what is french for twelve" Sebastian Roché was actually born in Paris, France and speaks fluent French.
Dean is just leaving 'Burger Heaven' when Sam calls. That is a neighboorhood family restaurant in New Westminster, a south-east suburb of Vancouver, BC, Canada.