an inconspicuous observer, a secret witness
I think there was a fly on the wall when I told mom about the Nigerian email that I had to delete.
someone who secretly watches something. like they're a fly on the wall and you don't notice them.
carlos knows that rosita's baby is really chico's thanks to that fly on the wall.
An unseen or unnoticed presence in a situation.
"Fly on the wall documentary" meaning a documentary where the cameras go unnoticed by the subject of the film.
"I wish I had been a fly on the wall at that meeting" meaning I wish I could have sat in unseen on that meeting.
to be present to listen/see what goes on behind closed doors, that is, in a room closed to the media or other non-participants
1. I'd like to be a fly on the wall when that (distrusted) union steward is making deals with management all on his own
2. I'd like to be a fly on the wall when my ex and her lawyer are talking about our separation agreement
3. I'd like to be a fly on the wall of suite 401 of the Best Western when my ex is visiting her boyfriend who's up here on business
a documentary that follows you around
i cant believe that fly-on-the-wall documentary caught me picking my nose