Black Butler (TV)

Starting from episode 14, the lyrics of the opening Monochrome no Kiss, change.

The Jack the Ripper murders happened in Whitechapel, England, which is exactly where they're said to have happened in the anime. The names of the Ripper victims mentioned are also correct. Most notably being the first victim, Mary Nichols who Ciel mentions as he speaks during breakfast with Madam Red, Lau, Sebastian, and Grelle. The final victim, Mary Kelly, was also somewhat accurately portrayed with her murder happening inside her room, rather than outside like the rest of the murders. Oh, and Fred Abberline was named after a real detective who worked on the Ripper case in Victorian England.

The color of Ciel's right eye, which contains his demon contract, is purple. This color may be a combination of his natural eye color, blue, and Sebastian's red eye color.

Episode 17, the opening has changed with different images but the same song.

Sebastian Michaelis got his last name from the Japanese word "mikairi" meaning "repayment."

in episode 11 the shop Elizabeth goes in has dolls resembling the Rozen Maiden dolls namely Shinku, Kanaria and Suigin Tou

In episode 17, when Undertaker is in the pot of salt, Sebastian holds his handkerchief to his nose. This implies demons have an aversion to salt, whether it be rock salt or just salt in general. This wouldn't be such an outrageous statement, seeing as some other shows, movies, and books (ex. Supernatural) say that salt is good for keeping demons at bay by sprinkling a trail in front of doors or windows to keep them out of a house.