Both times (before and after Clark reverses time) Lex throws his alcoholic beverage and glass into the fire in his mansion, there is a burst of flames that just appear to be larger. This burst should be blue as alcohol burns blue.
When Jonathan wins the election, his name is spelled incorrectly as "Johnathan" on the television in the background.
When Clark compresses the lump of coal to produce a diamond the result is a perfect brilliant cut diamond. What Clark should have produced is an uncut diamond.
It is snowing as Clark and Lana are talking outside in the open yet, no snowflakes land on either of them.
When Lana says yes to Clark's proposal in the Kent's yard on the screenshot of Lana it is snowing but in the screenshot of Clark it isn't snowing.
In this episode, Clark uses a crystal to travel back in time. Jor-El warns Clark that this can only be done once. Contrary to that statement, unless the Fortress travels back in time with Clark, the crystal that allowed him to time-travel would still be within the Fortress and would be unused later in the episode; which potentially allows for infinite time travel back to that or any other day.