After Sylvie and Erik have gotten gelato, whilst they are talking, Erik's gelato slowly disappears between takes and then reappears suddenly.
Opening a champagne bottle with a saber requires that you knock off its mouth (not just knock out the cork). For that, you need impact - and you get the most of it if you use the blunt side of a sword or a champagne sword (which are built blunt). Despite having performed this many times, Gérard uses the sharp side.