After the court-room scene, Karol Karol is throwing up, but we can't hear a "vomit splash", and there isn't vomit in the closet.
When Mikolaj hires Karol to kill him, Karol fires a gun into his chest, then says "That was a blank. The next one's real." While blank cartridges do not contain bullets, they can discharge a wad of cotton at high velocity (which is what killed actor Jon-Erik Hexum when he jokingly fired a blank into his temple). Mikolaj would have been severely injured if not killed being shot with a blank at such close range.
When our couple manage to make love, Dominique's moanings are not simultaneous with her lips.
When Karol first returns to his brother's salon after his arduous journey from Paris, he expresses delight regarding the new "neon" sign above the shop door. The brother confirms that, yes, he got a "neon" sign.
The sign is actually many incandescent light bulbs spelling out and encircling the name of the shop. There is no "neon" lighting.