Continuity mistake: When Desiree walks into Clark's barn to work on their 'student-teacher relations', she holds her hair up with her right hand as she complains about the heat. She then lets her hair down and fixes it. Cut to a different angle and she is letting her hair down once again.
Continuity mistake: In Jail, when the sheriff tells Chloe and Lana that visiting time is over, we see Clark holding the bars with his left hand as he tells the girls that his dad went to see Desiree. Cut to a different angle (from inside the jail cell) but now Clark is no longer holding onto the bars and only holds them a few seconds later.
Continuity mistake: After Lois and Clark find out that Cooper dies, and after Lois leaves, while Clark and Geoff talk about how Lois is trouble Geoff hair keeps going from neat to slightly messed up. When the camera is behind Clark, Geoff's hair is all shaggy on the left side of his face. When the camera is behind Geoff, his hair is fixed so that the loose strands are tucked behind his left ear. These changes repeat throughout the scene.
Continuity mistake: The bomb that Garret wears has four kryptonite section, one at each of the corners, and each section has three distinct pieces. The pieces glow only from the center core and the outer edge is only green colored and is not glowing. When the shot switches to the CG shot of Garret falling, The camera passes over and grabs the bomb and now the krptonite has a uniform glow and there are now the one block on each corner does not have the three individual pieces.
Visible crew/equipment: After Joseph gets locked out of the construction site, the worker, who locked him out, walks away. All the other workers at the site are gone, but when the shot returns to Joseph you can see the shoulder of someone standing between Joseph and the gate even though there should be nobody there.
Continuity mistake: When Jodie hits the deer her vehicle spins out. As it is spinning the headlights are not projecting any kind of visible beam. After the car stops, and she is facing the deer she hit, the headlight is now projecting a very bright beam to illuminate the deer on the road.
Continuity mistake: As Chloe is trying to get Clark to help her deliver presents Clark says "Chloe, you didn't have to go there." Right before he says this the two of them start rounding the corner to go down the next hallway. As he is saying the line they are back in the first hallway and start rounding the corner again.
Continuity mistake: During much of the conversation between Clark and Lana, while in the caves, you can see the cave painting that matches the tattoo on Lana's back is behind her. Then, towards the end of the conversation, she is still standing in front of Clark and during the scene has not moved from that position yet, once she sees the cave painting behind Clark she walks over to it and turns around to face Clark, which puts the painting behind her even though it was already behind her before she moved.
Continuity mistake: When Chloe and Lionel finish their discussion in the cave the shot focuses on the Naman/Segeth glyph and focuses through the glyph to a transition shot of an island that Lex is on. When we first see this island it is flat and covered with trees. The next time the island is shown there is now a large volcano/mountain that was not their when we first see the island.