1. Director Quentin Tarantino revealed at Comic-Con that Jamie Foxx and Kerry Washington's characters are meant to be the great great great grandparents of the character John Shaft from the Shaft movies. An overt reference to this connection can be found in Kerry Washington's character's full name: Broomhilda Von Shaft.
2. Leonardo DiCaprio, whose role in the film marked the first time him playing a villain since The Man in the Iron Mask, was uncomfortable with how horrible and explicitly racist his character was. However, Quentin Tarantino convinced him to be as menacing as possible saying that if he didn't take it all the way, people would hold it against him forever.
3. After an accident in training where Christoph Waltz was thrown off his horse and broke his pelvis, Jamie Foxx gave him a gift to make him feel better about riding a horse: a saddle with a seat belt.
4. The last name of Dr. King Schultz (Christoph Waltz) is a reference to Paula Schultz, the name on the gravestone that the Bride (Uma Thurman) is buried alive under in Kill Bill: Vol. 2.
5. In the scene where Leonardo DiCaprio's character Calvin Candie smashes the palm of his hand on the dinner table, the actor broke a glass under his hand and really began to bleed. DiCaprio ignored it, stayed in character, and continued with the scene. This take was the one used in the film.
6. Jamie Foxx used his own horse, Cheetah, in the movie.
7. Sid Haig was considered for the role of 'Mr. Stonesipher', so much so that casting director 'Victoria Thomas' informed Haig's agent "It's a lock". Quentin Tarantino himself scheduled, and later canceled at the last minute, two auditions for Haig. Two months later, the role quietly went to David Steen instead. Tarantino being known for his extremely dry humor, this "prank" is presumably rooted in Haig turning down the role of Marcellus Wallace in Pulp Fiction 17 years previously.
8. Franco Nero, making his cameo in the film, is seen wearing white gloves. This may be a reference to the original Django film where at the end Nero's character has his hands smashed by the Mexicans for being a thief. However; this should not be seen as him being the same character in both movies, as Django takes place in an unspecified time after Django Unchained and U.S. Civil War.
9. In an interview promoting the film, Quentin Tarantino stated that originally the mandingo fight scene and the scene with the dogs were longer and more violent. Quentin said he felt like he was going to "traumatize" the audience of the film so he cut both scenes down
10. Ultimately, Will Smith decided to pass on playing Django in the film due to him seeing the character as not being the lead. He told Entertainment Weekly, "Django wasn't the lead, so it was like, I need to be the lead. The other character was the lead! I was like, 'No, Quentin, please, I need to kill the bad guy!' ... I thought it was brilliant. Just not for me
That's incredible!