Unchained Melody - Can you spot the bass mistake?

My friend Artie Wayne has put together some Halloween related music videos, two of which I happened to play on. They were “Unchained Melody” and “Hell Of It” by Paul Williams from “Phantom Of The Paradise”. One of the things that always amazed me on the “Unchained Melody” session was the bass mistake. I heard it at the session but in those days there was no “punching in”. It was the best take and that’s how it was released. To this day, every time I hear it, I still cringe a little. Can you find it? Play the below video, leave a comment and take a guess, if no one gets it I’ll leave the answer in a week or so.