a fly on the wall

fly on the wall

One who is able to observe something closely but invisibly and without interfering in the situation. I would love to be a fly on the wall in John's house when he finds out his wife bought a new car without telling him.
See also: fly, on, wall

a fly on the wall

COMMON If you would like to be a fly on the wall when a particular thing happens, you would like to secretly hear what is said or see what happens. I'd love to be a fly on the wall at their team meetings. What I'd give to be a fly on the wall when Draper finds out what's happened to his precious cargo! Note: You can use fly-on-the-wall to describe something such as a documentary film (= film about real people and events), where the makers of the film record everything that happens. For six months, a BBC film crew worked on a fly-on-the-wall documentary about their forthcoming marriage.
See also: fly, on, wall