Plot hole: Miss Fisher and Samson have to find the right, narrow, timeframe to sneak into the ringmaster's tent and go through his belongings. But they seem to have an unlimited amount of time once afterwards, since they flat out take the big crate he has in plain view containing all sorts of incriminating evidence, and then have all their time to get to the station to bring the evidence to Jack, compare serial numbers, have a lab check on the vials, even dig up graves, all without Mr. Jones getting suspicious in the slightest.
Continuity mistake: Miss Fisher as 'Fern' is posing as the magician's assistant. He does the (supposedly, before the man in the crowd calls out 20 as grand finale) last throw successfully and walks up to her to retrieve the knives. They are obviously positioned differently between shots. (00:30:30)
Continuity mistake: Jack and Hugh are checking out of the serial numbers of the banknotes. It's quite obvious during the sequence that Hugh has a couple of wads in his hands, then he is hands free, and then is holding the same wads as before. (00:39:30)
Continuity mistake: In the faraway shot, the snake is wrapped around the neck of the dead body full circle, while in the close-ups that follow and precede, the snake is draped across its neck and creeps up the right side of the deceased. (00:01:20)
Continuity mistake: When Miss Fisher introduces Samson to Jack, the clock in his office shows it's 10 AM. When Senior Sergeant Grossmith is at the phone just outside, the time displayed is half past 8. (00:05:00 - 00:05:50)
Answer: Louisa's watch was broken during the struggle to get away from her attacker.
Bishop73