A friend of mine has since given me some more information on this saying. She says;
That means, to "Refresh myself while the demon (ogre) is
away" or "Wash my life in the demon's absense" in direct translation. This
proverb is usually translated into English as "When the cat's away, the mice
will play" because the image of the demon is a cat for a mouse. In other words,
in Japan, the image of the demon is a husband for a wife.
In Japan, generally, husbands are
bossy to their wives, so the wives are obedient to the husbands, on the
surface. Sooooo Japanese wives intend to refresh themselves while the
husbands are away on a business trip or something.
Another proverb might prove the
above opinion. "Teishu genki de rusu ga ii". This means, "It is best for wives,
both husbands' health and their absence". Japanese wives definately like their
free time, like me. That means enjoying travelling, theatres and learning
what you thought is natural, because Australian men are kind to their wives.
Australian husbands aren't the demon!
Thanks a lot for that Nakai-sensei!