Interestingly, during this musical episode, the two regular cast members of Fringe (2008) who have the most Broadway musical experience do not ever sing. Blair Brown (Nina) has had singing roles in Broadway productions of "The Threepenny Opera" and "Cabaret." And Michael Cerveris (The Observer/September) is better-known as a Broadway leading man than as a television or film actor; he has had lead roles in Broadway musicals such as "The Who's Tommy," "Titanic," "Assassins," "Sweeney Todd," "Lovemusik," and "Evita"; was nominated for Tonys for all but one of these; and won a Tony for "Assassins."
The trivia item below may give away important plot points.
The Observer is referred to as "Mr. Gemini" by Nina Sharp. This could be a reference to: 1. The identical "Gemini Observatories" located in Chile and Hawaii. 2. The Latin word for "twin", referring to the similar look of the observers and/or the twin persona we all would have in the parallel universe - a main theme of the series. 3. The Observers are named after months, of which there are twelve. There are also twelve zodiac signs, which loosely correlate to the twelve months.