So many things I didn't pick up on till after getting home. One of them was when Dean is showing Chris around the house and shows him the grandfather's photo and talks about how he lost the race to Jesse Owens, a black man... Dean literally says "he almost got over it." Seems like such a throwaway line at the time, but the fact he didn't get over it is literally the impetus for all of this.
Another little thing with a line that can be read two ways - it's at about 0:55 in this video:
"We hired Georgina and Walter to help care for my parents... when they died, I couldn't bear to let them go." he isn't talking about letting go of the help, he's talking about letting go of his parents... which he never did.