Continuity mistake: In Season 6, Episode 10, Dexter and Harry are in the motel room where Travis was staying (timestamp 1). Dexter decides to post on Gellar's blog (impersonating Gellar), and the screen on the computer shows the post date as Sunday, November 24, preceded by a Sunday, November 20 post. Aren't Sundays supposed to be a week apart? Then in episode 12 (timestamp 2), Travis is in Dexter's apartment and sees the poster for the Noah's Ark school play. The date posted for the play is Saturday, October 8, ie. in the past compared to the earlier episode. Plus If November 24 were on a Sunday, then October 8 should have been on a Tuesday.
Continuity mistake: When Dexter started removing the plastic off Travis' body, his small knife was stabbed into the chest, but during that, the sword was already stabbed into the chest, not the knife, and then again, he removed the knife from the body, and then stabbed him with the sword.
Continuity mistake: Dexter browses the book shelf at Travis' house. The camera pans across, revealing a book titled "Apocalypse Bound" situated at the right on the shelf. When Dexter takes the book off the shelf, it is then shown as the fourth book from the left. When he puts it back, the empty gap where it used to be now appears to the far right on the shelf.