Contrary to popular belief this is not the instructions that a Catholic aunty gives to pigeon in her balcony.
A Fly Man in theatre terms is a person who is part of a Fly Crew - the guys responsible for all the stage scenery that descends from above the stage.
The responsibilities of a fly crew include bringing battens in and out, keeping the fly system linesets in balance, and ensuring that the fly system's rope locks are applied when the associated linesets are not moving.
During a show, predefined cues may require flymen to operate the fly system at high speeds and with great precision.
The scenery used in shows can weigh up to one tonne and may be flown in at speeds approaching 30 miles per hour and stopped at stage level without hitting the deck.
It is an incredibly special skill and often takes years to master. It is rightly considered an art form in its own right.
Loaders are special flymen who work high above the stage in the grid, adding or removing counterweights from the fly system.
The job is often dangerous and carries a high degree of risk due to the large amount of weight and great heights involved.
A run-away line, for example, might injure the operator or others in the way of the moving equipment, and a counterweight dropped from the grid could kill or injure a person standing below.
When the crew adds or removes counterweights they are often working at heights of six stories or more in the area above a stage known as a fly loft, or grid.
Historically, off-duty sailors were used as fly crews in theaters because they had comprehensive knowledge of knots and ropes due to their experience with sails. They communicated with one another using high-pitched whistles.
Because of this, whistling was not allowed in theaters to prevent it from accidentally being interpreted as a flyrail command.
That is where the superstition emerged that it is 'bad luck' to whistle in a theatre.