Dumb Cats

Why is it they only act up when DJ is gone? He must really be intimidating to them, since they lay down and go to sleep when we lock them in for the night. But not when he is gone. They can be laying down and being lazy until i lock them in our room for the night and turn off the light. They are terrors, getting into everything and wrestling and just being pains. Nala will run around the table in the dining room to keep me from catching her. Gromit is the better behaved. He goes straight to bed and is only a trouble maker when his sister starts it.