Hi there! We are oxygen and Me and my friends want to pass through, can you let us in?
Hi, I'm Alveoli and to pass through you must enter me!
We are Red Blood Cells and we will guide you to the end of the passage!
Alright go through their when you are ready!
Why do I feel weird?
Oh, that's because when you pass through here you guys start to go bad and when that we start to feel the effect too. When that happens it is a signal for you to leave because we get hurt when you stay for too long