Jenny closes her eyes to find out what it's like for a blind person to light a cigarette. Meanwhile, the cigarette and cigarette lighter switch hands.
In her bedroom Joan sits on the side of her bed, takes a cigarette from a side table holding in her left hand with a lighter in her right. The camera goes into a close up and the cigarette is now in her right hand and the lighter in her left.
A blind pianist would not have sheet music stacked on top of his piano.
In the opening dance sequence Joan Crawford is wearing regular stockings, but in the close up of her leg a very different fish net stocking is shown.
In an old newspaper review, Ty rhapsodizes about Jenny's performance of the song "Tenderly" which he saw her perform on the night before he was shipped off to WWII (and subsequently blinded). In reality, that tune was not written until 1946, a year after war was over.