Angel and Gunn question a man in a comic book store. When they throw him against a stand of comics he says that they're "crushing the Dark Horses," referencing Dark Horse Comics, the company that publishes the "Buffy" and "Angel" comics. Before leaving the store, Angel is also seen reading a comic book with the Dark Horse logo visible on the cover.
One of the pictures Cordelia Chase puts up in Connor's loft is of her parents. This is the only time they are shown in the Buffyverse.
Almost all of the references to string theory, P vs NP and other physical concepts in this episode are real scientific terms and are used in the correct context-contrary to many other TV shows and movies.
The orange graphic novel that is shown on the comic book store rack is Hellboy, who is a well-meaning half-demon who is a paranormal investigator, like Angel.
When Fred sees the Symposium's "Featured Speakers," she exclaims, 'Oh, God! I'm between Ed Witten and Brian Greene!' These refer to Edward Witten and Brian Greene, two important physicists. This shows how important the speech will be that Fred gives.