The writers seem forget about Lanas necklace that she wears causes Clark to be sick in early season 1 and she is seen without it in several episodes before it reappears again.
In several episodes, an establishment shot is shown in scenes in the Kent's barn at night. A crescent moon is shown with its limbs pointing down toward the horizon. This can happen, but not at night.
Traffic enforcement seems a little lax in Smallville as we see teenagers aged between 14-15 drive vehicles in the early seasons. In the State of Kansas a 14-year-old can get a learner's permit to drive, however, Clark, Lana, Chloe, Pete and their classmates should have restrictions placed on there driving since Kansas law also states that an adult 18 years and older must be along at all times when they drive. So Clark and his friends are violating state law by driving alone and without adult supervision when the provisions of having a Restricted Permit even when 15 years old requires licensed adult supervision to drive.
There are license plates in the show that read Metropolis but license plates list the state the car is licensed in not the city.
Throughout the series, most of the actors playing teenagers are actually in their twenties or older. This is a common practice in television for several reasons:
- It helps avoid child labor laws that limit how long minors can work on set and allows production to continue without interfering with real-life schooling.
- Casting adults provides more experienced performers.
- It gives producers greater freedom in depicting mature or sexualized content.
- It offers teenage viewers characters they can relate to and look up to.
Because this series used different writers working on different episodes, there are several continuity errors regarding the characters ages for example:
- The writers in season one forget that Clark, Lana, Pete and Chloe are freshmen aged 14-15 and write scenes of them driving without adult supervision when they aren't even old enough to have had driving lessons.
- Lana is running her own coffee shop at the age of 15 when she is still a freshman.
Throughout the show's ten-year run, exterior shots of the Talon coffee shop have the letter O reversed on the sign. All other uses (on posters, flyers, other signs) etc. have it correctly oriented, including later-season shots of the sign through windows etc.
Closed Captioning on several episodes never matched what was said on television or purchased DVD iTunes. There are times one song is sung but CC sings another song.
It is incorrect to say that Kansas is almost devoid of hills. Only western Kansas is almost devoid of hills. The Flint Hills are located in eastern Kansas.
The exterior of Smallville High changes after the first four episodes of Season 1. This is because the first four episodes were filmed at Vancouver Technical Secondary School, while episodes 5 through to the end of Season 4 used Templeton Secondary School. The two buildings have noticeably different architecture, but both are meant to represent the same school. In fact, stock footage of the original location is occasionally reused after the switch, creating visible inconsistencies between shots.
In Redux (2002), Lana is said to have been born 1986. In Crusade (2004), the tombstone of Chloe Sullivan gives her year of birth as 1987. In Aqua (2005), Clark identifies himself as 18 (placing his birth in 1987). It is never explained why Lana is in the same class as Clark and Chloe, when she is a year older.
Some characters are seen commenting on Clark's "blue eyes", but in this series he is depicted with Tom Welling's natural green eyes.