Spoof of the movie, "The Defiant Ones" starring Tony Curtis and Sidney Poitier.
The hound is playing "Red River Valley" on a harmonica.
The bus has a destination of Sing Sing, a nickname for the penitentiary at Ossining, New York.
As in the feature film, the moral of the story is, enemies or not, they're in this together. The Star Trek: The Next Generation (1987) episode The Enemy (1989) would also use this premise.