Revealing mistake: When Anna (little girl who stutters) is crying after being teased, the "tears" on her cheek are obviously fake. They never run or move. I'm guessing rubber cement.
Little House on the Prairie (1974)
1 revealing mistake in The Music Box - chronological order
Continuity mistake: When Mary and Laura dive into the lake to rescue the puppies they have their shoes on. As they are swimming around looking for them they are barefoot. When the get out of the water their shoes are back on.
Laura: I wanted to clean the blackboards extra good today, to make up for being late.
Mary Ingalls Kendall: And talking in class?
Laura: I was not talking.
Mary Ingalls Kendall: You were, too.
Laura: Was not! Nellie was talking and I was answering.
The Voice of Tinker Jones - S1-E11
Trivia: Sean Penn is in this episode, albeit with no lines, always wearing the same blue shirt. His father directed this episode.