When Johnny comes home drunk, his collar changes throughout the scene from being flipped up in the back to being properly placed.
When John and his wife eat chicken and drink milk in the middle of the night, John puts the cap back on top of the milk bottle. In the next shot, he still pours milk and there is no cap on top of the bottle. He puts the bottle down on the table and does not affix the cap on top of it.
Around minute 29, Jane Mason asks her Doctor's nurse for a paper and envelope. Nurse gives only a sheet of paper - no envelope. Jane writes a love note, attaches a safety pin then folds the note into thirds. She stands, picks up the note and her purse and leaves. Late represents an envelope to John Mason in the courtroom.
When John Mason (Jimmy Stewart) visits Judge Doolittle's home in the middle of the night, as John is pleading with the judge's brother Simon to wake up the judge, Simon mouths the exact words John is saying as he is saying them, showing his memorization of the script.