Sam mentions he saw an objection from the trial on "The Good Wife". Jeffrey Dean Morgan who plays John Winchester, Sam and Dean's father, went on to play Jason Crouse on that very same show a few years later.
After the second unexplained death, Dean says, "Alright so what, he causes so much misery that some rottweiler goes Cujo on him from beyond the grave?" He referring to the 1981 Stephen King (and subsequent movie) of the same name about a rabid dog.
The trivia items below may give away important plot points.
The setting of this episode is Dearborn, MI. When Dean and Sam find out they need a ram's horn to use against Osiris, Sam says "where are we going to find a ram's horn in Dearborn?" There is a chain of restaurants called Ram's Horn in and around Dearborn.
When Osiris confronts Dean, Dean says, "I'd rather talk about your Bukowski shtick at the bar." He is referring to Charles Bukowski (1920-1994), poet and novelist whom Time magazine called a "laureate of American lowlife."
Body count: 4 Matthew Hammond - run over by a ghost car, killed by Osiris; Christopher Fisher - mauled by ghost dog, killed by Osiris; Warner - shot by ghosts, killed by Osiris; Osiris - rendered dormant, stabbed with ram's horn, killed by Sam Winchester