This question gets a variety of answers in our house.
One day while I was in the kitchen and C was in her high chair, suspiciously quietly eating yogurt --
Me: Caroline, what're you doing?
Caroline: Making a mess.
One day while I was in the living room and C was in the kitchen, coughing repeatedly --
Me: Little C, what're you doing?
Last weekend, while we were driving home from Chattanooga, C was in her car seat "reading" a book. I noticed she'd had it in front of her face a really long time and hadn't turned the page in a while --
Me: C, what're you doing?
Me: Oh Caroline, can you wait til we get to a potty? Can you hold it a few minutes?
Caroline: I can hold my horses, Mama.
PS. She did and we made it to the potty! Thank goodness we were 1/2 a mile from a rest stop.