➞ 
when occasion arises
When the cat are away the mouse will
when the cat is away the mouse will
when the cat's away the mice will play
when the cow come home
when the cows come home
when the going gets tough
when the going gets tough the tough get going
when the going gets tough, the tough get going
when the gun roar the Muse be silent
when the guns roar the muses are silent
When the cat are away the mouse will
when the cat is away the mouse will
when the cat's away the mice will play
when the cow come home
when the cows come home
when the going gets tough
when the going gets tough the tough get going
when the going gets tough, the tough get going
when the gun roar the Muse be silent
when the guns roar the muses are silent