The pistol used in several scenes by Captain Lewis and Captain Connaught-Smith was a revolver. The time frame for this film was set in the 1820's. The revolver wouldn't be invented and patented until 1836.
When Captain Lewis is tied to the ground, a reflection is visible between him and the cobra, revealing that a pane of glass separates them.
About 36 minutes into the film, Captain Lewis messes up his grammar when he tells Colonel Henderson, "It is you who are making the terrible mistake". The grammatical sentence is "It is you who is making the terrible mistake".