"-- cancelled on me. I don't have anyone to give the shiur (Torah class.)"
"There's something I had been thinking about..."
"I'll check with one more person, and if that doesn't work out, I'll let you know."
Duhh!?! What had I done? I volunteered to give a shiur? Gevalt!
Yes, I did it on Shabbat. It was very participatory. Nobody dozed off.