Continuity mistake: After the credit card company calls the Kent's to confirm purchases made the night before, we see Jonathan holding a mug by the rim. They then notice the music coming from Clark's barn and go to investigate. Cut to a different and now Jonathan is holding the mug by its ear.
Continuity mistake: Chloe is sneaking around inside the warehouse that Lex is using to hide the space ship. After she is found by a security guard she turns back around to look in where the ship is. When she does a shot from her POV shows the fan blades spinning faster then they were in the shot before and after when we are looking at Chloe through the fan.
Plot hole: When Nixon and Jonathan are trapped in the crypt after the landslide, Nixon says he can't breathe, and Jonathan says this is because the landslide cut off the air supply. However, we can see beams of sunlight shining in. So, unless the ceiling of the crypt is made of airtight glass, that landslide didn't cut off the entire air supply.
Continuity mistake: When Clark is fighting with Dr. Walden, twice Dr. Walden sends Clark flying, with his powers. Both times, when Clark hits the ground, he becomes quite buried into the soft dirt, not entirely, but relatively sunken into it. However when it will cut to the next shot, Clark is lying on the dirt without being buried into it at all. This is obviously due to switches between actor and stunt double.
Continuity mistake: As Lana says "I was thinking the same thing but we don't seem to be very good at it." there is a camera change as she says "but". Before the change she only has the red cup on the tray but after the change, even though she didn't pick it up, she has a red and a yellow cup on the tray. The other cup was on the table and jumps to the tray between shots.
Continuity mistake: After Dante says "...if you want to turn that tortoise into a hare just give me a call." he walks off and the shot follows him as he walks all the way over to a black car and starts to work on it. The shot returns to Clark and Pete and Dante is shown walking away again on the left side of the screen.
Continuity mistake: At Ryan's surprise welcome back party, Clark puts his right hand over Ryan's shoulder as he asks him "you knew about this didn't you?" Cut to a different angle as Ryan responds "I was tempted too" but now Clark's hand is no longer on Ryan's shoulder. Cut to Clark then back to Ryan and now Clark's hand is back on Ryan's shoulder.