When Chloe's father picked up the phone to answer the call from Lionel Luthor, Clark was behind the chair Chloe's father sat on. After Earl started shaking, Clark was shown sitting next to Lana.
The plunger Martha is holding changes from black to red as the camera angle changes.
When the students are released from the LuthorCorp plant, Pete's words don't match his mouth while he's talking to Martha.
When Earl visits his baby, it clearly shows hard shadows from the mobile attached to the baby's crib, suggesting that the light should be right above it, but when the shot switches to the baby's viewpoint looking up, there are no lights to be seen.
When Whitney uncovers Earl in Clark's barn, Clark mistakenly calls him "Pete" when he tells him to stop before Whitney skewers Earl with a pitchfork.