The movie is published with a punctuation error in its title. "Eight Legged Freaks" means "eight freaks with legs" and is pronounced with only three syllables in total. The correct punctuation is "Eight-Legged Freaks" meaning "freaks with eight legs" with four syllables in total ("legged" with two).
When the line goes dead while Deputy Pete is on the phone with the Sheriff, he has the receiver in his left hand, but when he goes to tap on the phone base, there are clearly two hands holding on to the base. When the shot goes back to his face, he is still holding the receiver with his left hand.
When the people are running into the mall, Wade asks what's going on. Later, he turns and runs back in the mall. We see a shot of the entrance of the mall, the front gate is half-way closed and closing. In the next few shots the gate is completely open. Later, Chris turns a key and the gate starts closing.
In the mall, when the sheriff is fighting the spiders by himself, he sees the big one come on the ceiling and drops his gun and runs. Later, when he is surrounded and goes under the bars, you can clearly see his gun in its holster.
When the giant tarantula is attacking the silver radio van, the spider is seen attempting to roll the van over. After a few scene changes the van is pictured from above on its side. Yet in the next scene the occupants within are still standing relatively upright on the floor of the van. The following scene change then shows the van being tipped onto its side.
In the mall, the Sheriff closes a roller grate but the spiders reach through and catch him. He operates a chainsaw to chop off the legs holding him, and in the process gets showered in the face with green spider goo. This shown in close up, but in the following scenes, his face is clean and dry.
In the beginning where Chris meets Aunt Gladys in the office there is a dog biting at his pants. During the shot between his legs, the arm of the animal wrangler can clearly be seen pulling the dog forward by the collar.
When they are in the mall and the spiders are just about to break in, the woman goes "Get ready." And she looks behind her and tells everyone to get ready. When she does that, you can see the green garage door to protect them from the spiders already torn apart for the scene when all the spiders start coming in.
The driver of the truck taking the hazardous waste to the mine listens to the radio show on an AM station. Later in the deputy's car, they listen to the same broadcast on an FM station. However, it's possible that Harlan was broadcasting at both modulations.
When Sam is in Mike's room and notices the film on the TV, he is watching Them! However, the television shows scenes from the movie taken out of their chronological order and spanning the entire length of the feature film.