After Smith is passed the bread plate at his first supper with the sisters, it disappears and reappears on the table between shots.
After Homer Smith leaves the nuns the first time, they have to walk to Mass - apparently a fair distance. When he returns, he picks them up in his car as they are walking to Mass but they still arrive just as Mass is beginning. They should have arrived much earlier as they thought they were walking the entire distance.
When Homer returns after his unexplained absence, he turns the car around and overtakes the Mother Superior. From a distance, it is obvious that he overshoots her by about fifteen feet, but the next shot shows he stops with her directly outside his car window.
When Smith starts to sing the final song he seems to have a cleaner shirt than the preceding scene.
When Homer leaves the nuns for the first time, the nuns must walk to mass along the road downhill. The sun is shining left to right across their faces casting a shadow on the ground to the right of screen. In all close-ups of the nuns, the sun is shining right to left (the complete opposite direction) across their faces.
When Homer orders breakfast in Juan's Trading Post, he asks for toast with Strawberry Marmalade. Marmalade is only made from citrus fruit; all other fruit becomes a jam, preserves or jelly.
When the pickup truck arrives loaded with bricks. The tires and suspension are barely strained. If the truck were loaded with as many bricks as it appears, the truck would be overloaded, the bed would be riding very low and the tires would be pressed down.
In the last scene when Homer is about to leave the sisters, they sing Amen. It is obvious that their voices are dubbed. Their lips are not moving to the music.
When "Schmidt" first takes the nuns to mass and he goes across the street to breakfast and orders pancakes, Juan pours the pancake batter on the griddle and continues his conversation with Smith. At no time does he ever flip the pancakes over and yet they don't burn.
The record the nuns use to learn English, uses a speaker that clearly doesn't know anything about German. This becomes especially obvious since the nuns all speak German perfectly, so they should wonder about this weird pronunciation.
In the beginning when Homes pours water into his car's radiator, the engine isn't running. That risks cracking the block. Presumably the engine was running hot because Homer knew it needed water.
When Homer is climbing down the ladder after finishing the steeple, one can see the 3 spaces in the brick (the top rung of the ladder cuts across the top space).
When the nun is looking up verses in her large Bible with Homer, she obviously isn't turning to the correct passages. Proverbs is near the center of the Bible (not in the first 20%). When she turns to Matthew, it's closer to the end of the Bible than Luke was, despite Matthew coming before Luke.
Sidney Poitier "sings" throughout the movie. In his autobiography, he states he is tone-deaf- unable to sing on key.
After Homer gets a drink of water from Mother, as he pulls away in the car, the camera's shadow is visible on the car. Also a large white rectangular reflector is reflected briefly in the window.
The sign on the restaurant where Homer eats his breakfast on Sundays is misspelled as "Juan's Tradeing Post."