After Karel Novak has played the Hollenius Cello Concerto and is receiving an ovation, as he acknowledges the applause, his cello appears and disappears. In the closeups, as he takes his bow, he has it, but when the camera cuts to him in long shot, it is missing.
When Christine is putting out the candles after the wedding party, at least one candle is relit between shots.
When the three principals are first seated at their table in the French restaurant, there are many camera shots, and the waiter upturns the upside-down water glasses to fill them too many times.
When Christine returns home and Novak is practicing, there is a heavy downpour of rain seen through the window. But Christine, who entered with packages, shows no signs that she had been out in the rain. She has no umbrella and her clothes, as well as her packages, are dry.
When Christine confronts Hollenius in his bedroom, he slams the same newspaper down twice.
A "dress rehearsal" is one where a production is run through with all aspects of the final performance (other than the paying audience, of course). At the dress rehearsal for the concerto, no one is wearing performance clothing, the lighting is full up, and the set is not arranged as it is for the actual performance.
(at around 1hr 35 mins) At several points during the concert while Novak is performing, a bit of female hair can be seen sticking up over his left shoulder. In addition, his left-hand looks like a female hand. Apparently, the double crouching behind him handling the fingering aspect of the cello performance is a female musician whose hair was not completely hidden.
There is no blood on the evening clothes of the person who is shot, either prior to death or after falling down the stairs.
While Christine, alone in her studio, is talking to Alexander Hollenius on the telephone, the highly visible shadow of a crew member is moving back and forth across the piano behind her.
On several occasions, Karel and Bertram are carrying their cellos in non-protective, soft cases, even outside in a downpour. This would be highly irregular for performers of their caliber, who typically would be using quite valuable (possibly vintage) instruments and carrying them in rigid cases.