Director Trademark (James Wan): [puppet]: (At around 30 minutes) When Josh is in the classroom, on the chalkboard behind him, the name "James Wan" can be clearly seen, as well as a drawing of Billy, the puppet from Wan's Saw (2004), with the number "8" written under it.
(At around 30 minutes) When Josh Lambert (Patrick Wilson) is dismissing his class, the names "Yesim Osman" and "Leslie Borchard" can be seen written on the chalkboard. Leslie Borchard was a hairstylist for this film, and Yesim 'Shimmy' Osman was the hair department head.
Josh's mother in the film is named Lorraine. Coincidentally, Patrick Wilson (Josh) would later go on to play Ed Warren, husband of Lorraine Warren, in "The Conjuring", which was also directed by James Wan.
This is the second project involving horror where Barbara Hershey stars in, after The Entity (1982). In that film, Carla Moran (Hershey) is pursued by an evil being. Curiously, in this movie, her son Josh, played by Patrick Wilson, is pursued by an evil being.
James Wan, who directed both Insidious 1 & 2 and The Conjuring 1 & 2, had The Conjuring franchise in mind, while directing the first Insidious movie. A number of coherent points can be spotted in both the first and the second Insidious movies
At around 1 hour and 12 minutes) Josh looks through several pictures of his younger self when he finds out that he can astral project. In one of them, he can be seen carrying a dog, which belongs to director James Wan.
In the scene where Dalton sheets are covered in red handprints, it is mistaken for blood, but is actually red lipstick. The red faced demon (known as the "lipstick demon", using his hands to apply his "signature red look") leaves the handprints, showing how close he already was to Dalton at this point in the film.