Continuity mistake: In the scene where Sarah and Chuck find the suspected bomb, Sarah initially tries to disarm it by removing the numeric key pad under the display. She leaves the keypad off when she goes over to talk to Chuck. In the shots where the characters are talking, the keypad remains off but every time the shot changes to a close up of the suspected bomb the keypad is back on, under the display. (00:37:00)
Factual error: When Chuck and Jill recover Guy LeFleur's hard drive containing the list of Fulcrum agents, General Beckman says that the flash drive is encrypted with a 512 bit AES cypher. She then goes on to state, "the computer is trying every possible key against the encrypted data, " i.e., a brute force hack. However, it would take the fastest supercomputer in the world longer than the existence of the known universe in order to crack even a 128 bit AES encryption (and a 512 bit AES encryption has the number of possible keys of a 128 bit AES encryption, raised to the fourth power). In a previous episode, Chuck refers to the computer in Castle as having a "30 teraflops" speed, which is far less than the current fastest supercomputer. General Beckman instead says it will take only hours or days. (00:26:10)
Revealing mistake: In the scene where Ellie is testing her Thanksgiving turkey by giving Morgan a piece, when she throws it in the trash he says 'no no no Sarah.. what are you doing!', which is the actor's name (Sarah Lancaster), not her character's. Maybe edited in some versions. (00:09:40)
Plot hole: Casey needs to get Devon's hospital keycard in order to get into the secure holding area to plant the listening device into the pacemaker before it's implanted into the terrorist. They obtain the key-card by stunning him at his bachelor party and see Casey using it to access the storage facility, backed up by Chuck and Agent Forrest. We then see the terrorists scanning their leader and detecting the implanted bug - Devon is listed as the surgeon. Immediately after this, we cut to Devon waking up from his bachelor party with his keycard missing. None of the three agents involved in planting the bug could possibly have handled the operation, no other agents are mentioned as being present and, as the break-in occurred during the daytime, the staff of the busy hospital would have noticed had an unknown surgical team suddenly taking over one of their operating theatres. So Devon apparently got into the hospital with no key and did the operation while completely unconscious.
Continuity mistake: In the scene with Orion working at his computer in Hong Kong and the Fulcrum agent is coming, he is watching Chuck, but he hears them, closes the window and its blank, but then the immediate next shot the screen shows Chuck still, and then the next shot it is black again. (00:02:10)
Continuity mistake: The yellow pen that John Casey stabs into Ty Bennett changes between shots after Ty pulls it out. As he rotates it in front of the camera we can see that the bold BUY MORE logo is only printed once. Still in the very next shot, not only has the text changed direction (reading from the hat-side to the tip-side now), the logo have also appeared in front of Ty. (00:05:50)
Continuity mistake: Sarah is making Chuck a frozen yogurt using a banana and a knife. Take notice when Sarah cuts up the banana, the slices are disorganized while she is talking to Chuck. However, when Sarah decides to pick up the slices of banana, the pieces are now nicely organized.
Factual error: When they first bring Grueber into Castle, Sara states that "he is one of five people who can hit a target from half a mile away." Half a mile is 880 yards. Basically every person who has graduated from (or likely everyone who has been selected for) sniper school in any military in the world should be able to do this. (00:05:20)
Continuity mistake: Near the end when Jeff and Lester confront "Greta" in the cage she pulls out her knife. Jeff attempts to disarm her but she cuts off his tie. She cuts it very close to the top, leaving very little around his neck, but when it cuts back to him after showing the piece hit the floor there is much more tie left.