Some years ago I travelled a route very regularly. I would often doze off while we were sitting on the tarmac. I had watched the safety video dozens and dozens, possibly hundreds, of times. One day I was in a little daydream, probably about to nod off, when I realized that the safety announcement wasn't the same as it usually was and they were saying something very different about how to fasten your life jacket. Nothing about waists and double bows - this was all about legs and clips! This aircraft had completely different lifejackets. I didn't know how to use them and I was about to spend 3 hours flying over water!

I have watched the safety demo and paid attention to it ever since.