Actors have a superstition of not whistling in dressing rooms - Why?

Answer 1

Actually the superstition is not to whistle backstage.

The reason is that back in early theatre, curtains were raised by dropping heavy bags. Whistling was a signal to raise the curtain (thereby dropping a bag), so the people backstage new to stay clear.

So if anyone whistled backstage one of the heavy bags would drop, either seriously injuring or killing them. Now that's back luck.

Answer 2

Just an addendum to DramaGuy's answer, which was spot-on as usual:

The reason sailors communicated in whistles is that the wind would carry away any shouted orders. Whistles can be heard above the din of the shrouds and sheets on a sailing ship.

Answer 3

No whistling!
In the olden days, stage hands were out–of–work sailors (theaters and ships share a profusion of ropes) who communicated with complex whistles. So, if you were walking around stage whistling a tune, you could accidentally call down a sandbag onto your head!

Answer 4

Whistling evokes the spirit of The Scottish play....*whispers* Macbeth. Never whistle, never say Macbeth and never say goodluck...say break a leg. The 3 theatre rules.

Answer 5

And never bring a yellow chair into the green room!

Answer 6

DramaGuy has it right, but I thought you might like some links that include other superstitions:

http://www.kclibrary.org/guides/arts/index.cfm?article=read&articleID=518

http://lecatr.people.wm.edu/theatrical_superstitions_and_saints.html

http://en.wikipedia.org/wiki/Theatrical_superstitions

http://www.nicoth.com/articles/test_your_know.htm

There are tons more of course, but I'm sure that's good for now.

Enjoy!