Continuity mistake: Prior to bringing Ray up for the role-playing exercise, the parenting teacher erases a circled phrase from the chalkboard. Throughout the scene, the chalked circle flips several several times between being totally erased and having a faint outline left over.
Visible crew/equipment: When Dewey yells for Lois because the bow was put on the present, if you look to the left of Lois, you will see a crewmember kneeling down, handing Lois the Red Dress, who is holding a bucket of water. He quickly gets out of the camera's view. [This is on the DVD of the first season. Someone said on the audio commentary that after catching it, they deliberately left it in to see if anyone would spot it. It's still a mistake, but that's why it's there.]
Continuity mistake: When Mr. Roper tries to explain to the girls and his wife what he was doing in Jack's bedroom, watch over Mr. Roper's left shoulder on the shelf. The number of yellow cans on the shelf keep alternating between one and two cans throughout several minutes. In addition, also notice the suitcase on the floor under the shelf as well. Whenever one yellow can is shown, the suitcase is by itself and whenever two yellow cans are shown, there is a square silver bag in front of the suitcase.
Continuity mistake: Vera fires the gun several times, and later tells Justice Wargrave that the gun is empty, meaning that all the cartridges in it would be spent. When the judge loads his one bullet into the chamber, he does so in a gun where all five cartridge svisible are unspent.
Factual error: A thief has stolen 75 million dollars. He runs out with two large duffel bags. All US bills weigh a single gram. This means that $1,000,000 in $100 bills - the largest bills in circulation - weigh around 10 kilograms, or a little over 22 pounds. $75 million would be 1,650 pounds. No way this could be carried in two duffel bags.