Sleipnir's eating carrots in this episode is possibly a reference to the fact that he was actually Odin's horse in Norse mythology.
The name of this episode is Unfinished Business. Among many other references to Kill Bill: Vol. 1 (2003) in this episode, whenever "The Bride" is about to face one of the 5 people on her revenge list, she tells them they have unfinished business.
Dean compares to Gabriel's mission of revenge to Kill Bill: Vol. 1 (2003), one of director Quentin Tarantino's best known films. The dialog, action scenes and plot of this episode were also written and filmed in the style of a Tarantino film.
Michael Adamthwaite (Narfi) also played Security Guard Bill in season 7's The Girl with the Dungeons and Dragons Tattoo (2012).