When Judge Harley Nast and other members go up into the organ loft, the judge carries a red lantern, which he places on the player's bench of the organ. Later everybody leaves, yet nobody picks up the red lantern and takes it away. Later still, Luther returns to the organ loft: no red lantern is seen, but now the loft is lighted by candles in a candelabra.
When Don Knotts steps between the trees at the picnic in his honor, the tree just to his left is a eucalyptus tree. Eucalyptus grow just fine in California but would not grow in Kansas where the movie is set.
In the newspaper article about the anniversary of the murders that took place in the mansion there are duplicate columns on either side of his story. Also, several of the newspapers seem to be yellowed with age.
When Luther is setting up his sleeping bag, it is obvious that the light from the flashlight is coming from off set. The light shines on his back when he is in front of the flashlight even though the flashlight is on level with his knees.
When Luther lands in the coal bin, he gets out of it and there is no coal dust on his clothing. His clothes are perfectly clean and anyone who has been in contact with coal knows that coal dust gets on everything it touches.