Factual error: Lana is trying to find out what Lex is up to. She gets a hold of his briefcase and takes it to the mansion where she shoots the locks off the case. When she does the case jumps a little bit but this is far less than it should. She is shooting at it from less than a foot away. The force of the bullet should have sent that case sliding across the desk at that range.
Continuity mistake: The blood on Lana's face is different then how it was in the previous episode. While at the crater in Commencement she has two distinct lines of blood on her face. One on her left cheek is thick and the one on the right cheek goes down past her lips. While at the crater in this episode the left line is then while the right line is shorter. These two scenes should be identical since Arrival picks up right after Commencement.
Continuity mistake: When Clark decides to stay home from school because he cannot control his heat vision, his father decides to have a talk with him. Jonathan pulls his son to face him and them places both his hands on Clark's shoulders. Cut to a different angle as Jonathan says: 'Clark, look at me ' but now we see his left hand on Clark's neck. Cut back to the previous angle and his hands are on Clark's shoulders again.
Continuity mistake: When Dr. Hamilton was about to pour liquid kryptonite on Clark, Pete hits him on the back and he goes crashing onto a table knocking everything on it off the table. Yet later we see an open bottle of liquid kryptonite on the edge of the table (which was cleared by the doctor earlier) dripping onto the doctors forehead.
Continuity mistake: While Clark is chained up, Chloe uses her fingernails to dig into Clark's chest. You can see that since Clark has had his powers taken away her fingernails draw blood. In the shot of Clark screaming in pain you should see where the blood came from the scratches but there is no blood visible.
Plot hole: Justin's power is telekinesis, which he uses to attack the doctor at the beginning of the episode. He shows that he is targeting the doctor's hands by blacking them out on the drawing, but he has absolutely no way to see what is happening in the elevator to know the exact moment when to drop it and cut them off.
Continuity mistake: When Lex is talking to Lionel outside the building site at the end, Lex's sunglasses disappear while the camera is on Lionel and reappear when back on Lex. This happens after Lionel turns to face slightly behind Lex and continues throughout the rest of that exchange.