The coffeepot Mike brings to the table when he first meets Joyce is suddenly completely empty at the end of the scene, despite having far more than two cups worth of coffee in it to begin with.
Joyce crumples up the note from Mom, throws it in the fireplace, leans on the mantelpiece for a moment, then pushes herself away so hard that the entire fireplace shudders, causing a plant on it to shake, and revealing the entire fireplace wall to be a prop.
When Trudy, the teacher, phones Lt. Manners, she only dials five numbers, instead of the six numbers that had been used for another call in the same town earlier in the film.