Revealing mistake: Having been deserted by their porters three white people and a native journey on. During their journey an antelope is shot by Allan Quartermain for food. The sound of the shot is dubbed in as there is no recoil from the high powered rifle he uses.
Continuity mistake: After the bearers leave the group, they head through the jungle to the Karawana village. There are only 5 people and they're carrying what they can, having left most supplies and equipment behind. All of a sudden a couple of lions appear and run by them. They duck out of the way, but in the long shot as the leopards are running by there is a pile of packs and equipment in front of the group. One lion jumps right over the pile of gear. There should be nothing on the path in front of them - the bearers all went back the other way. (There is the chance that the gear is left from Henry Curtis, the person they are trying to find, but it would be a major find and a major plot point and the gear is never mentioned or shown again).