zai jian.i>>> if you want to know how much a hummingbird weighs, check your pockets. a hummingbird weighs about what a penny weighs -- less than one tenth of an ounce. >> medical emergencies happen. that's why knowing what to do is so important. ♪ >> what is "cpr?" >> cpr stands for and that's a really big term that basically means cardio -- heart; pulmonary -- lungs, resuscitation -- try to bring back. we provide a combination of chest compressions and rescue breaths to manually circulate blood throughout somebody's body. because when they are in cardiac arrest it means their heart's not working, so we need to work for it. >> is it something that we all can learn? >> absolutely, in a real red cross course when you take the full thing, you learn how to give breaths, but absolutely anybody can learn how to do hands-only cpr. and that's what we're gonna practice today. >> okay, i'm ready. >> step one, we want to make sure this person is actually unconscious,