or long enough to be a chorus. For example, refrains are found in the Beatles' "She Loves You" ("yeah, yeah, yeah"), AC/DC's "You Shook Me All Night Long", Paul Simon's "The Sound of Silence", and "Deck the Halls" ("fa la la la la"). The chorus or refrain is the element of the song that repeats at least once both musically and lyrically. It is always of greater musical and emotional intensity than the verse. "The chorus, which gets its name from a usual thickening of texture from the addition of backing vocals, is always a discrete section that nearly always prolongs the tonic and carries an unvaried poetic text." In terms of narrative, the chorus conveys the main message or theme of the song. Normally the most memorable element of the song for listeners, the chorus usually contains the hook. Post-chorus An optional section that may occur after the chorus is the post-chorus (or postchorus). The term can be used generically for any section that comes after a chorus, but more often refers to a section that has similar character to the chorus, but is distinguishable in close analysis. The concept of a post-chorus has been particularly popularized and analyzed by music theorist Asaf Peres, who is followed in this section. Characterizations of post-chorus vary, but are broadly classed into simply a second chorus (in Peres's terms, a detached postchorus) or an extension of the chorus (in Peres's terms, an attached postchorus). Some restrict "post-chorus" to only cases where it is an extension of a chorus (attached postchorus), and do not consider the second part of two-part choruses (detached postchorus) as being a "post"-chorus. As with distinguishing the pre-chorus from a verse, it can be difficult to distinguish the post-chorus from the chorus. In some cases they appear separately – for example, the post-chorus only appears after the second and third chorus, but not the first – and thus are clearly distinguishable. In other cases they always appear together, and thus a "chorus + post-chorus" can be considered a subdivision of the overall chorus, rather than an independent section. Characterization of a post-chorus varies, beyond "comes immediately after the chorus"; Peres characterizes it by two conditions: it maintains or increases sonic energy, otherwise it's a bridge or verse; and contains a melodic hook (vocal or instrumental), otherwise it's a transition. Detached post-choruses typically have distinct melody and lyrics from the