Other mistake: Early in the episode, Clark uses his heat vision to blow up a police car. In the shot where we see the policewoman diving for cover, there is a front view of the car as it is exploding. The license plate on the front of the car IS a Metropolis plate, however, as the plate falls off, the white placard that auto companies and dealerships place in the license plate frames on new vehicles before they are registered and which are removed once plates are installed is visible.
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.