This was what I can come up with.

Somehow, I did another poster, which is more intuitive to most people, as the previous is more cultural bias. It has the same text and with the same "Save Life" slogan, I took a photo from the squeeze ball I got from donating blood last February in NUS, which is really a blood bag-shaped.
It shows that the pulse was really erratic and when it goes in and out of the blood bag, it becomes stable and normal. I hope it is more intuitive and easier to understand than the previous as it requires some explanations to most people who do not know about it.