This is the first episode where Chris does not appear. He does, however, appear in the animatic version of the episode, dressed as Meg for the costume party.
This is the second episode which the show discusses Stewie's talking and that certain characters may or may not be able to understand him. The first was "E. Peterbus Unum".
Brian is shown as an atheist in this episode. However, in "If I'm Dyin', I'm Lyin'", Brian says to Peter, "You want an explanation? God...is...pissed!" while slapping Peter across the face with each word because of all the events that were happening. Similarly, he is more intolerant about religion in both this episode and "Not All Dogs Go To Heaven" than in "Movin' Out (Brian's Song)".
The book that Brian wanted to get out is The God Delusion by Richard Dawkins.
At the Halloween party, Peter and Lois repeatedly say "Laura Bush killed a guy". Laura Bush did in fact kill a guy. In 1963, 17 year old Laura Welch ran a stop sign at an intersection and crashed into another car, killing the driver, Michael Douglas. No charges were made against Laura Bush.
When the scene in the library turns to Brian a book has the All Seeing Eye on it.
Stewie seems to have another homosexual moment around Brian in this episode when he starts to put his finger in Brian's mouth and then suck on it with his own mouth.
Brian and Stewie are both dressed as Snoopy from Peanuts. Brian does Snoopy's trademark dance, and also has Woodstock following him.
Lois' yoga trainer is dressed as an aborted fetus, but Brian thinks that she is one of Freddy Krueger's victims.
Joe is dressed up as Mark Spitz, but because he is in a wheelchair, all of his friends think that he is a crippled Magnum, P.I. because of his hair and mustache.