When JJ and Reid are in the morgue, there's a sign that says "OXYGENO". It should say "OXIGENO", the proper spanish translation for "OXYGEN"
Alex: The unsub made Ridgeway look like a saint. He even used his own kid to bait the victims.
Morgan: Well, we've seen that before. No doubt we'll see that again.
Morgan references "In Birth and Death" where the unsub was using his child as bait to lure victims as well.
Garcia's rant about Agent Blake reveals she was recruited by the FBI at the age of 24, is a professor of forensic linguistics at Georgetown University, graduated from Berkeley with a double major and a doctorate, and was a star in the Unabomber case. Later, Blake demonstrates her fluency in American Sign Language (ASL).
Jeanne Tripplehorn joins the cast as Supervisory Special Agent Alex Blake in this episode. She joins Thomas Gibson at the end of the opening titles sequence and is added to the group photo at the end of the sequence. Tripplehorn is billed as "with," and Gibson is still assigned "and" billing.
While at D.C.'s fictional version of Comic-Con, Sci-Fi Gate, Reid dressed as the Fourth Doctor (Tom Baker) – long scarf and fedora – while Garcia dressed as the Eleventh Doctor (Matt Smith) – bow tie and fez.
When a student asks why he never heard of the serial killer described, Morgan names three others that never received national attention: Efren Saldivar, David Parker Ray, and John Edward Robinson. All of them were real serial killers at one time or another. Of the three, only Ray was never convicted for his crimes.
The character David Zimmerman (portrayed by Zack Weinstein) was named by Virgil Williams as a shout-out to fellow writer on the show, Bruce Zimmerman.
The case presented in this episode was loosely based on Henry Lee Lucas, who was convicted of murder in 11 different cases and was once listed as America's most prolific serial killer. Lucas died in prison on March 13, 2001 from heart failure at the age of 64.
As Prentiss and Morgan chase a suspect, she radios in that the suspect is moving at a high rate of speed north on Van Buren. Enid Oklahoma (where this episode is set) has at least three different streets named Van Buren: Van Buren Avenue, Van Buren Place and Van Buren Street.
Around the 27-minute mark, Garcia brings up a map showing where a grocery store is located. Instead of Chicago, it's a map of Rockford, Illinois, which is about a 90-minute drive from Chicago.
Cindi introduces her son, Anthony, to Morgan as his Uncle Derek. However, if Cindi is Morgan's cousin, then Anthony would be Morgan's second cousin (or cousin once removed) and not his uncle.
During this episode, Laura Heathridge's left arm is missing and she wears a prosthetic limb. At the end of the episode, she opens the door to a mystery man using a real left hand (not seemingly part of her delusion), then also reaches to the man using a real left hand. It could be argued that her real left hand is part of her delusion, but if this is the case then she should have had a real arm from the moment the doorbell rang (presumably also part of her delusion).
Reid mentions the drowning test to discover if someone is a witch was used during the Salem witch trials. That is incorrect. There were never any kind of tests performed on supposed witches in the infamous 1692 trials; they were convicted based only on accusations and spectral evidence.
The challenge coin that Morgan gave to Angel as well as all the coins on Morgan's desk belongs to Jim Clemente.
Margaret: (to Tommy) King Henry the 8th's first wife was much older than he was.
Catherine was only twenty-four, though, while he was eighteen.
When the team arrives at the unsub's house and Reid steps out of the car, Matthew Gray Gubler is wearing unmatched socks, which is the actor's trademark.
The opening scene of this episode almost exactly mirrors the kidnap scene in the movie Taken, including some of the dialog, the girl hiding under the bed with a cell, a bad guy entering the room and her scream.
In keeping with the "8" theme, the signal Spencer sends is given the encryption code H8-88. "H" is also the 8th letter of the alphabet.
The number 8 appears to be significant in this episode: In the final showdown, the mirror in which the unsub sees himself is an octagon (8-sided), the chandelier behind Rossi has 8 arms, all the windows in the house have 8 panes of glass, and the couch has 4 seats making 8 cushions on it.
During the opening scene, the attacker brings music on a USB drive to play. Herman Scobie was the copycat who attacks the Piano Man's victims the second time, but he misses part of the Piano Man's M.O. and does not play the piano ballads.