Third Rail Projects has a rich production history of placing its audiences on the cusp of collaborative theater. Its dancer-actors are the clicking wheels of a larger machine; they are not themselves the stars of the show, but let an almost spiritual illusion take over that billing. In the long-running hit Then She Fell, experiential theater transcends all of its normal bounds to create just that illusion. The production, which is written, directed, designed and choreographed by Zach Morris, Tom Pearson and Jennine Willett, is a haunting take on Lewis Carroll's book "Through the Looking-Glass," and it derives every last morsel of dark lyricism from its source material.