Continuity mistake: The doctor starts out carrying a Holland and Holland "Royal" Double Rifle; but when he and Tarzan pursue the train, the doctor loses his H&H rifle in the leap from a cliff. Lo and behold, after they commandeer the train and disembark, the doctor is inexplicably carrying his H&H Double Rifle again. The H&H is not a common rifle, even today, and his chances of just discovering an exact replacement aboard the train is beyond coincidental.
Factual error: Virtually all of the CGI animals in this film are rendered at about 150% of their natural size. Additionally, even a small gorilla could tear the strongest human limb-from-limb, so Tarzan wouldn't have lasted two seconds in a hand-to-hand combat with an alpha male gorilla.
Factual error: Near the beginning of the film, Greystoke exits Number 10 Downing Street after speaking to the Prime Minister. Downing Street is shown as a busy thoroughfare with many people walking by. But, in reality, Downing Street is a cul-de-sac (a dead end) so would unlikely to have ever been that busy. Incidentally, the public right of way into Downing Street has never been revoked despite 21st century security measures restricting public access, which is possibly technically illegal in UK common law.