(at around 40 mins) Olive oil can't be instantly ignited by throwing a flaming torch into it. It won't burn until it reaches over 500 degrees Fahrenheit. Phineas' statement about olive oil was right, as it does burn quite nicely as a fuel oil, but it does not produce acrid black smoke.
The buildings of Rome are shown as pristine white stone. In fact, Romans painted their buildings in garish colors.
(at around 9 mins) Obvious stunt double as Jeffrey races away in the senator's chariot. The stunt double is wearing a wig that is much darker and much curlier than Jeffrey's hair.
During the gladiator arena scenes at the beginning, crew equipment becomes visible. A light and a vehicle can be seen past a doorway when the director's credit appears on-screen. These items are also visible in the wide shots of Bogg and Jeffrey being pushed forward by guards.