The language that Magnus speaks while summoning the demon is Chthonian.
The scratch on Simon's forehead may appear to switch sides between scenes, but only if you don't notice that he's looking into mirrors.
Magnus's line about the Dead Sea and his response to Clary's question about Jace's state are both quotes from City of Ashes.
Cassandra Clare's first set visit was on the last day of shooting this episode.
Simon mentioned Kirk Duplesse, a member of his band in the books.