When Clark shows up to school and asks what's going on, the new principal states that the gate locks when school starts and doesn't open back up until school ends. But this doesn't make sense because right before this, Lana states that she has the first 2 periods off. How would her or other students that have the same type of school schedule as her, get into the school without the same trouble?
When Lex and Mr Reynolds are speaking after Clark walks away, the latch on the parking lot gate goes from open to closed & locked between scenes.
When Chloe pulls up the file on Troy, it says his date of death is June 20, 2002. This can't be possible unless they have spirit week in the summer, which is highly unlikely.
Lana assumes that since the dates on the photos of her mother and the other man are after her parents were married, that there must be something suspicious about the couple. Dates on the backs of photos merely show when the photos were developed. They could have been taken years before.
While speaking with the principal after dropping Clark off, Lex mispronounces "enmity" as "emnity."