Revealing mistake: When Charles Ingalls plays his fiddle at the end of the episode, one can see from the movement of his hands that he is not really playing, but just pretending. (Also visible in every other episode where Charles plays the fiddle, but most obvious in this one.).
Revealing mistake: When Carrie (played by twins) falls down in the opening sequence, it appears that she gets back up and continues running. In reality, after falling, the other twin gets up and continues. If you look closely enough, you can see that when getting up, Carrie is slightly closer towards the camera than when the first twin fell.