A: Leaving her behind after a stop.
On our first ride of 'spring' last weekend, I slowed and stopped where the rail grade trail we were on crossed a road.
Seeing that the way was clear, I announced "Three, two, one, we're off!" and pedaled across the road. "Wow," I thought, "She's so smooth, and it's our first ride of the year. This is going to be a great season." The bike accelerated especially well and I was very impressed with the apparently effortless power from behind.
After about a quarter of a mile, I looked back to be sure that the other rider with us was on our wheel. I got a very clear view of Carl about a hundred yards back, pedaling for all he was worth to catch up and yelling, "I think you forgot something."
Somehow I did not notice when my stoker slipped off the bike to walk over and press the walk button for the cross walk. Fortunately, upon my hasty return, she was laughing pretty hard. I had no idea it was even possible to ride off without noticing one was solo...
You learn something every day I guess.