Go on for a ride in the woods to wade in the creek, and (ten minutes after you get there) tell your mom you have to go potty. And not just toilet-paper-preferable potty, but toilet-paper-imperative potty. She will tell you it's time to go home. Here is where the face comes in. Your sister will pull a face too, because she doesn't have to go and won't understand your plight. These are the "times that try the soul."