Factual error: During the "skull monologue", Calvin Candie mentions "genes". The word was coined after 1905 from the work of Danish scientist Wilhelm Ludvig Johannsen. Genetics were born with Mendel's work, which was published in 1866 and did not become widely known in the scientific community until decades later.
Continuity mistake: During the first shootout scene inside Candiland, when Django rolls off Leonide Moguy (Candie's Lawyer) he rolls to the right of the shot, away from the room he had just come from. However in the next scene when the door is kicked in we see Django moving and shooting from the opposite side of the room, towards the side he should already be.
Continuity mistake: After first arriving at Candieland, Calvin Candie is explaining to Steven who Django is and that they will be staying in the big house. During this scene, cuts between Calvin and Steven show Calvin's legs alternating between crossed in one angle and uncrossed in the other angle, multiple times. The lawyer's arms also go from being crossed to uncrossed when Calvin does the introductions between Django and Steve.
Continuity mistake: In the scene where Django shoots Smitty Bacall, the plough that he is using can be seen on the far left of the field and moving at a slow pace. But when Dr Schultz puts his wanted poster away, the plough is suddenly on the far right of the field having not had enough time to have turned round and moved that far.