When they walk through the hallways at school, Hallie and her classmates put bubbles in their mouths to help them remember not to talk to one another. (Just so you're not worried, they actually just hold air in their mouths and puff out their cheeks to make it look like they have bubbles in there.) Hallie's really good at putting bubbles in her mouth, to the point that once I saw her hang on to the same bubble for 12 minutes straight.
Now, whenever Tom and I ask Hallie to take her volume level down a notch or to simply be quiet for a couple of minutes, she automatically puts a bubble in her mouth. It's like her "I can be quiet" security blanket.
She stayed like this for an entire car ride home, and it was the most peaceful car ride we'd had in quite a while.