Revealing mistake: Near the end after Django shoots "Moonlight" and two other guys, Moonlight is on the floor in pain. When he squirms around he puts his right arm out, revealing a wire from under his shirt going up his right arm. Most likely this was used to ignite the squib charge on his right shoulder. (The first shot Django made in this scene was shooting Moonlight in his right shoulder). (02:36:50)
Continuity mistake: When Django is shown looking at various hats, he tries on a top hat. It is level on the stand when he picks it up, and when he puts it back it is now at a noticeable slant. After some dialogue the shot comes back to include the hats and the top hat has become perfectly level once again.
Continuity mistake: At the beginning, Jamie Foxx's scar on his forehead comes and goes as the white man picks him out of the chain gang.
Continuity mistake: Ace Speck's hat changes positions while he lies dead and Django and Schultz move around the place.
Answer: Django and Schultz killed some of Big Daddy's farmhands, and he wasn't going to let a freed slave kill some of his workers. Schultz knew Big Daddy would come after them for what they did. Plus Django would never let go of a chance to kill a slave owner who was trying to kill him.