With the cool cat away, the mendacious mouse would play.
Or even a string, which mouse will play with and hope to take back to the nest.
In the old days, the assumption was that when the cat's away, the mice play.
While the dragon is away, the mice do play.
When the cat's away, the mice will play and when the teacher left the classroom the students began to move around.
Don't tell me the mice haven't been playing while the cat's elsewhere.
When the cat is away, the mice will play.
Maybe they could catch the mice playing if they thought the cat was on the other side of the planet.
As I said the morning of Peter's departure, when the cat's away the mice will play.
"When the cat's away, the mice can play," he said.