Dr. ramirez examined 100 brother–sister pairs for 10 minutes each, note on a checklist the behaviors that occurred during 20 thirty-second intervals. this is an example of

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.