According to Don Knotts's autobiography, the off-screen voice yelling, "Attaboy, Luther!" belongs to screenwriter Everett Greenbaum.

This film inspired a short-lived craze for yelling out "Attaboy, (name)" during speeches and other situations. This came from a running gag used in this film. The Farrelly Brothers used the same gag in Kingpin (1996).

The film earned $1,245,684 during its first week of release, making it the #1 top grossing movie of the week.

The "Simmons Mansion" was next door to the Munster Mansion on the Universal back lot. It appears, without the fence, in the opening credits of Munster, Go Home! (1966). However, the Munsters house doesn't appear in this film.

An uncredited script consultant was brought in to authenticate the Haunted House conspiracy based on an episode of "The Andy Griffith Show." That consultant was in fact Andy Griffith.

Continuity

Halcyon's dessert cup is full, empty, then full.

One of Alma's fork tines is broken off then it is back on.

When the jury visits the Simmons House, not only has the painting of Mrs. Simmons lost all the cobwebs it had when Luther last saw it, but Mrs. Simmons has a completely different hairstyle.

The sandwich the "jell-o" man is finishing in the diner switches hands just as Luther tells Alma of the dead whale that washed up on the beach in San Francisco.

Outside the boarding house, Luther is talking to Alma Parker, who is sitting in her convertible. In the background, the lawn sprinkler in the yard across the street changes position between shots.



Factual errors

There is no prosecutor in a civil trial. As counsel for the plaintiff, Lawyer Whitlow is free to call any witness that the judge allows.

In the beginning, Luther takes a picture in the night with a Speed Graphflex and a flashbulb. He rapidly says, f32,... With that f stop, the film would be way underexposed, and even with flash, it would be extremely dark and useless. The setting may be a factual mistake, but it's perfectly in keeping with Luther's bumbling character.

It would be impossible for the organ to play any music after sitting for twenty years with no one caring for it or keeping it tuned. Since everyone is either carrying flashlights or candles around the Simmons Mansion when they visit it, one could assume that there was no power connected to the house as well. Pipe organs require air which is pumped from a system of bellows below the organ which help regulate the sound. Without power in the house, the organ would have been useless.



Incorrectly regarded as goofs

When Luther is spending the night in the murder house, he sees shears stuck in the throat of the woman in a painting with blood gushing from the wound. Later, when touring the house during the trial, the painting is unmarred and without blood stains, but it is never explained how this was possible. It's implied that Kelsey, the former gardener, had a duplicate painting made and substituted the reproduction with the shears stuck in the throat for the original painting of Mrs. Simmons, and then switched the untouched original back on the wall after he had frightened Luther with the reproduction that had the shears and the blood on it.

At the beginning of the movie, Calver Weems is smacked on the head with a board (presumably by his wife Edna June, who leads him to the jailhouse). However, on the street, when Luther is frantic with Susanna Blush - the board is present, Calver is present, but Edna June never steps out from the bushes. But Edna is wearing gloves when whacking Calver with the board; evidently she stayed in hiding so as not to be seen as his assailant.



Revealing mistakes

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.

Obvious stunt double in coal chute.

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 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.

When Luther runs downstairs from the attic, the light from the flashlight shining on the wall doesn't match where he is pointing the flashlight.



Miscellaneous

The words to the big story about Luther staying in the murder house that everybody reads aloud don't match what's written on the page on the prop newspaper in the close-up.

After everyone from the court has left and Luther is climbing the stairs because he heard the music again, there's a stained glass window on the staircase wall with a bird design in the center of it, but the bird is upside down.

During the trial, the court stenographer keeps looking up at the people and not writing down what is being said.

Obvious stunt double: When Luther falls into the elevator.



Errors in geography

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.



Plot holes

When the organ in the attic starts playing by itself, keys move on every keyboard, instead of just one set of hands playing.