When the man at the boxing match offers George a slug of whiskey, a close-up shows him holding the bottle with the front label facing the camera, but in the next mid-shot, the back label is suddenly facing forward.
George blows out all but one of his birthday candles. When the view changes from over George's shoulder to a position over his father's shoulder, all the candles are out, but when it changes back, the one candle is again lit.
The magazine racks outside the corner store are mostly issues contemporary to 1951, with one glaring exception. A copy of the famous first issue of The New Yorker (published in 1925).