Each Friday night I drove my wife to the train station so she could go visit her sister who was ill. Ten minutes later, my sister arrived by train so that she could help with the house and kids over the weekend while my wife was gone. On Sundays this procedure worked in reverse with my sister departing by train 10 minutes before my wife arrived.
One evening after my sister left and while I awaited my wife's arrival, a porter sauntered over.
"Mister," he said, "you sure have some system going! But one of these days you're goin' to get caught!"