The reasons to flock to see Water for Elephants are not your typical musical theater must-haves. They include thrilling circus artistry and innovative puppetry, and, for those in the know, experiencing the adaptation of a beloved book-turned-movie-turned-theatrical romance. The touring company’s edge-of-seat daring was on display on opening night, as performers were tossed and caught, or were hanging and tumbling by a figurative thread, with only each other as a net.