Revealing mistake: When Agent Hotchner receives a text from JJ while interviewing the suspect, it is actually a screenshot. You can see Camera Roll in the upper left hand corner, "2 of 2" where JJ's name should be, and the Share/Play/Delete banner at the bottom. It is covered by Agent Hotchner quickly tapping on the screen to clear the banners. (00:16:15)
Revealing mistake: When showing the corpse's neck where the puncture marks are, you can see her pulse. (00:16:38)
Revealing mistake: When the unsub is in the house with the mother and her toddler, one of the shots of the toddler is flipped, before he starts crying.
Revealing mistake: When Hotch and Spencer are interrogating Eddie, Spencer shows him the three photos of the people he has killed. Eddie makes a gesture as if to speak and points at Spencer, at which point we see a shot of Spencer and he very obviously glances into the camera.
Revealing mistake: When the suspect is first put in handcuffs at the house, it's clear to see he is just holding the one cuff rather than wearing it. (00:27:50)
Revealing mistake: We see the jet at the end, and the shot is flipped. Note the serial number on the plane's engine. (00:38:05)
Revealing mistake: Just as Vincent gets tazered, you can see protective padding that he is wearing. This is not to be confused with his jacket. (00:25:10)
Final Shot - S9-E3
Revealing mistake: As Reid explains human reaction time, near the end of it you can see a brunette woman get hit and fall to the ground, she hits ground with the back of her head and then, while supposedly been shot dead, moves her right hand in under her head.
Revealing mistake: When Morgan is typing "Cult named Forever People," his phone is typing it automatically. His fingers aren't even tapping the correct letters. (00:19:45)
Answer: "The Boogeyman", s02e06. Spoiler alert: The kid is Jeffrey Charles and at that point he had already killed 3 other kids. Jefferey basically hated and resented other kids after his mother abandoned him and his father spent a lot of time with other children because of his job. Jeffery would lure kids Into the Woods and then beat them to death with his bat just because of hate, no particular "reason." The scene you're describing, Jefferey agrees to walk Tracy home when her "buddy" leaves her (at this point the FBI announced there's a serial killer on the loose and kids should walk with a buddy). Jeffrey gets mad at Tracy for walking too slow and for complaining, and he takes a swing at her, causing her to flee Into the Woods and have Jeffery chase her.
Bishop73