Meet My Master's Mother - S3-E9
Revealing mistake: The "ocean" behind Tony and his mother is a painted backdrop; the waves aren't moving. (00:20:10)
There Were Giants in the Earth - S1-E5
Revealing mistake: The Robot's lights wink out for a few seconds as it disables the force field.
Revealing mistake: Oliver and Eb cast shadows on the painted backdrop as Mr. Haney drives up.