Working together
When you make complicated movement, such as running and jumping, you use many different muscles at the same time. Leg muscles push you along, arm muscles help you to stay balanced, and muscles in your back hold your body upright. Continual repetition of a movement decelops your ability to make all these muscles work together.

Making faces
You have more than 40 different muscles in your face. You use them all the time when you are awake, and sometimes when you are asleep. They help you to speak, eat, and blink, and they also enable you to alter your expression. For humans, facial expressions are very important, because they allow us to show oyher people how are we sleeping. Babies know how to smile and laugh, but we learn many other expressions as we grow up. Try making faces at a friend, and see how many different feelings you can communicate without using words.