The Fool- Feste represents the contradictory nature of the play.  Though he is the fool, he has an incredible wit, and shows that things are not always as they seem.

Twelfth Night- The name of the play is a holiday in which things are said to be turned upside down.  Because of the nature of the plot of the play, this seems fitting. 

Music- The opening line in the play shows that music is an important metaphor for love.  Feste, at different intervals during the play, sings songs that help to illustrate for the audience the feelings of the characters at that juncture.