When Dr. Morrissey is delivering fish to Judy, she mentions that George is dying. Dr. Morrissey starts laughing and sits down, taking his glasses off.
In the next shot the glasses are back on.
As George is reading the newspaper during breakfast, the pages facing the camera change from shot to shot, even though he has already laid those sections down.
In the breakfast scene at the beginning of the picture, the level of coffee in Judy's cup constantly changes between shots. Also, the coffee starts out black, then later has cream in it.
The level of the sand in the toy truck that Arnold is filling.
George takes three colored pills before breakfast; the last one being pink. By the next shot, it has turned blue.
Arnold cautions George about cholesterol while eating nuts. Fact is, nuts have no cholesterol.
When Winny calls to hit on Judy, the shot of his face is footage reused from an earlier scene, specifically the one where he first demonstrates his 'foolproof technique.'
When Doris Day pulled Paul Lynde away from the door in the final scene, Paul lost his balance (either from tripping over the luggage or from Doris being over zealous) and near fell down. That clearly was not planned, but Paul made a nice recovery and kept the scene going.