Polystyrene balls

In the station where I worked there was a corridor separating the main open plan office from the rooms occupied by the gaffer and boss. Opposite the boss's door was an A4 size laminated sign showing the layout of the building and its emergency exits. We all now the building like the back of our hands, so no-one really pays that much attention to it. For years it has been stuck to the wall with blue tac. Never moved. Never interfered with. Until one night.

For some reason, I can't recall why, the sign drew our attention one night shift. Peeling it away from the wall we found it had been strategically placed, not because it was a good place to an emergency exit route card, but because it covered a hole in the wall that looked as if it previously housed an electrical switch of some description. The perfect square hole in the wall with nothing there now. Imagine what we could do with that? 

Well it quickly became the source of much hilarity. A bit of planning and searching for the right product and we decided that it would be a good idea to fill the hole. Nothing unusual or funny about that I hear you say, but we decided to create a bit of fun.

Carefully positioning the laminated sign to expose only the very top of the hole, we carefully (but not carefully enough) poured in tiny polystyrene balls. Unfortunately, they went not only into the hole, but everywhere else as well. Thinking we were being successful we suddenly noticed loose particles rolling gently under the boss's locked door. The quicker we moved to stop the flow, the more air we moved and the faster the balls rolled to an unrecoverable position, guaranteed to give away the plot before it could be set. 

Compromising and only part filing the hole, the laminates sign was then returned to its original position covering the hole and thus stopping the polystyrene balls from falling out. The only difference - the sign was now deliberately positioned upside down. With much hilarity, we managed to "access" the cleaners cupboard and vacuum the rogue polystyrene from under the boss's door, leaving the whole place looking like nothing happened. 

Imagining that despite having perpetrated this act of wanton fun, we would fail to see it taking effect, we finished nightshift expecting to hear all about it the following evening. 

Silence. Zilch. Nyadda.

Nobody said a word and no-one even asked if we had been responsible. A discrete check established that the sign was still intact and upside down. For weeks it remained so, until one day the gaffer did notice and, thinking he would merely turn the sign the correct way, ripped it from the wall only to be faced with a deluge of tiny polystyrene balls that covered the floor. Naturally, he was not best pleased and his wrath was clearly evident, but having just come into the building, we were viewed as the least likely candidates and so could achieve plausible deniability and believable innocence. Rants later the culprits remained at large and merely slipped out on patrol to consider and plan the next little escapade.