A: "The [session] is about to start."
Me; "Thanks, I'll be along in a few. You go ahead."
A: "Well, they're waiting for you. I rather think they were expecting you to chair it."
Me: "What!" (runs)
I really enjoyed it, too, even though it was very hard work, and most of the audience consisted of fearsomely intelligent people. I took the position of "facilitator" to heart, and just threw out questions rather than trying to say anything intelligent. *grin*