When the footpath killer initially confronts Gideon, he pumps his shotgun chambering a shell. Later, when Gideon is goading him to increase his stutter, the killer pumps his shotgun again, chambering another shell but the previous shell is not ejected.
At 06:03- the gasoline magically leaps up off the carpet and covers the student from head to toe.
When Reid is explaining the OCD, he says the professor's class was on Tuesdays and Hotchner says "Third day of the week."
Tuesday is actually the second day of the week.
In the beginning of the episode when reviewing the video tape J.J. identifies the burn victim as 'Matthew Rowland' however in the end credits he is listed as 'Matthew Cooke'.
As the gas station clerk is walking outside you can clearly see the window cling showing you have to be 19 years of age. This window cling is showing the age for alcohol purchase in the province of British Columbia and is was supposed to be taking place in Dumfries, Virginia.
Reid says that the involuntary repetition of one's own spoken words is called "palilia". The phenomenon is actually called "palilalia".
Hotch says that Clara counted off the ingredients of the light bulb bomb. But Clara actually counted off the ingredients of a Molotov cocktail, not the light bulb bomb.
During the evacuation / rescue at the burning building midway through, emergency crews and students are seen hurriedly fleeing the harrowing disaster. Yet, as people are shown descending an outside stairwell, one student is clearly grinning from ear to ear while he runs for his life, an unfitting expression for the circumstances. Not a speck of soot or sweat or singe anywhere on him, either.
While discussing the precursors to homicidal behavior, Elle mispronounces 'triad' as tree-ad.