When the cat's away, The mice will play.

People may relax the rules or indulge themselves when the person who normally supervises them is absent. The proverb casts that freedom as an opportunity they are quick to seize.

It can suggest harmless fun or mild misbehavior, depending on the situation. Its point is not that the absence causes trouble, but that oversight had been holding certain impulses in check.

Use it when a group becomes less disciplined after a supervisor or other watchful figure leaves. It can be playful about a brief lapse in routine or gently critical of people taking advantage of the absence.