Mark Ellen and I are doing one of our Word In Your Ear evenings tonight. It's a standing joke that half an hour before we begin Mark will start yawning. He's done it for years. Since the yawning will often coincide with a period of frantic preparation on my part it can give the impression that one party's trying and the other one isn't.
Yesterday I was listening to the commentary from the World Athletics Championship and a number of retired runners and jumpers were saying that when they know they're about to perform "your body withdraws to conserve its strength and you start yawning".
I passed this on to Mark and he sent me this clip of the Beatles getting ready to perform at Shea Stadium, just over fifty years ago. I never knew the pre-performance yawn had such a rich history.