I suspect we'd be somewhat underwhelmed by what S.W. and other would term 'mass hysteia', I watched it being 'induced' on television once, I'm probably wrong with this as it was years ago but I think it may have been the Royal College Christmas Lectures.
They prepared the episode by telling the audience that they were about to revel the worlds most potent scent, there was the usual dressing it up as one thing while it being quite something else, including anouncing the scent concentrate belonged to some company like Channel and having it brought in by two security guards.
The audience were told that the lecture was about how fast minute particles travel in air and upon removing the cap anyone who was aware they could smell it should immediately put up their hand.
I'm sure there would be some who didn't but most of the audience did, only then was it revealed that the container had nothing more than water within it and that the episode was induced by suggestion.