I'm a red blood cell

Recently, Maddie was a red blood cell carrying oxygen through a giant's body.  You didn't know that?  It's true.  She started the journey in the giant's heart, then traveled to the lungs to pick up some oxygen, and back to the heart.  Since this giant was walking, she needed to carry the oxygen all the way down to the giant's foot, where she then traded the oxygen for carbon dioxide, a waste product.  The carbon dioxide then needed to travel to the heart so it can be sent to the lungs.  Once the carbon dioxide was in the lungs, the giant exhaled, sending it out of the body.  Then, she was able to pick up more oxygen and repeat the process. 

There were four pieces of paper and a cardboard tube spread out on the floor for this activity.  Each paper had either a nose, lung, heart, or foot drawn on, and the tube was the trachea.   In the picture above, she had just carried the oxygen to the foot and exchanged it for carbon dioxide.  In the picture below, the oxygen is traveling down the trachea to get to the lungs.

She originally had 5 oxygen (red) and 5 carbon dioxide (blue) cubes to work with, and she did a couple rounds of this.  About a week after we did this activity, she impressed me by remembering how to pronounce carbon dioxide, what it is, and talked about it in the correct context without any help.