It was very crowded at the show, and rowdy too. I was told that the Phish show 9 months earlier at the same venue was sparsely attended. I guess a lot of people had been "educated" in that timeframe, me included.
Regarding the laughter from Trey during Cavern, it was actually that a girl jumped up on stage just in time to be nabbed by security at the exact moment Trey was singing "Taking turns at grabbing her."
I also remember lots of crowd participation during Forbin, including waving of hands in the air to simulate the waters of the Great Mississippi.
Loved the show, got me hooked for the next 20 years (and counting)....