Continuity mistake: During the flashback that happens at the Luthor mansion, the one that starts with the cup shattering on the floor, young Lex is shown peeking through a slightly cracked open door. Just after Lionel asks the nanny to give him Julian there is a shot of Lex peeking in and you can see that he has hair on his forehead. Now Lex, at this point, would have been bald, as a result of the meteor shower in Smallville for several years and would have no hair at all on his head in this flashback. In fact when Lionel finally realizes that Lex is outside the door we see that Lex has no hair on his head.
Continuity mistake: As Clark is sitting in his barn's loft his mother enters while he watches a model of the solar system. In the shot when he turns it off the large red globe, which looks to be Jupiter, stops well to the right of the model's sun in this shot. When the shot returns to Clark, Jupiter is now partially in front of the sun. Clark had not moved his hand from the off switch so he didn't move the model by hand and the model would have taken longer to make another rotation to put in that position.