Character mistake: Sam describes the books as being from "pre-Biblical lore" and then says they are written in Aramaic. Aramaic was a language during New Testament Biblical times and didn't exist in pre-Biblical times i.e. prior to 4000 B.C.E.
Suggested correction: I believe he meant the book "contained" pre-biblical lore.
Character mistake: After Alexis has White Knight Queen attack Sparkman and then has Snow Fairy attack Card Trooper, Jaden tells her that Sparkman's ability activates, which allows him to draw one card. This is not correct; it is actually Card Trooper that has the ability to let him draw one card, not Sparkman. (00:06:44)
Episode #5.3 - S5-E3
Character mistake: The chief baddie spells definitely as definately.
Character mistake: The note Six hands the "access man" misspells the word "receipt" as "reciept." He's supposedly a "think tank" genius, so really should be able to spell better than that. (00:27:30)
Episode #4.1 - S4-E1
Character mistake: Ruth tells the Oxford professor that she read "Classics" at Oxford. That's a major mistake - Oxford doesn't offer "classics" as a course: it is called "Greats" (or "Lit Hum"), and is referred to as such by the students reading it. It might be one thing for an Oxford alumnus to call it "Classics" when speaking to someone not at Oxford, but they would never say it to a member of the Oxford faculty.
The New and Improved Carl Morrissey - S1-E2
Character mistake: The advertising leaflet for the cemetery misspells it "cemetary" on the front cover.
Character mistake: Voice on the radio says a 39-year-old with a gunshot to the left shoulder; however, Will was shot in the right shoulder. (00:40:13)
Compromised - S1-E9
Character mistake: When she and OA meet Marshal Ackerman, Maggie is somewhat surprised to learn Damon Cruz was a federal witness. As a federal agent herself, Maggie surely would know that the Marshals Service's mandate includes the witness protection program.
Episode #3.4 - S3-E4
Character mistake: DS Miles while in the chocolate shop tells Ana to go with "DCI Riley." Riley has the rank of DC, not DCI.
Angel of Mercy: Part Two - S1-E4
Character mistake: When Lenore Osgood is speaking on the phone with Charles Wainwright about killing Dr. Hanover, she mispronounces "Larynx" as "Lar-nix."
Champion vs. Creator, Part II - S1-E27
Character mistake: Pegasus says his toon world cannot be penetrated, but that is not true since it's a magic card, so any card that destroys magic cards can destroy it. Furthermore, monster special effects can also destroy it.
Devil Music - S5-E4
Character mistake: When they pulled the bullet out of the wall of the Five and Dime, Danny says that it was either a .40 or .45 caliber. The .40 caliber was not produced until 1990, 37 years after the date the crime took place. (00:30:00 - 00:35:00)
Character mistake: In the epilogue, Charlie illustrates the relationship of mathematics to real life by discussing the golden ratio and its presence in a host of real-life situations, including the shape of a nautilus shell and the distribution of petals in a flower. These claims are disputed by some mathematicians (see http://en.wikipedia.org/wiki/Golden_ratio#Nature), and the one about the nautilus shell one is untrue (see http://en.wikipedia.org/wiki/Golden_spiral#Spirals_in_nature). It's possible Charlie is just repeating what he has read or heard without investigating it for himself, but this is uncharacteristic of him.
Character mistake: A police officer describes a murder weapon as a revolver. It is an automatic pistol.
Episode #2.3 - S2-E3
Character mistake: DS Maxwell comes to Katy's house to interview her but when he introduces himself he says "DI" Maxwell.
From Agnes - With Love - S5-E20
Character mistake: Using a Texas Instruments TI-89 Titanium, the seventeenth root of 9,000,355,126,606 is 5.781163783, which means the first prime number greater is seven.
Second Time - S2-E13
Character mistake: When Kiera is begging one of the Freelancers to send her back she says she could "prevent Liber8 from ever coming to 2077." She should have either said "coming to 2012" or "leaving 2077."