"Unloaded" guns are no joke, they are very dangerous, because so many times, they're not. Rule # 1 applies.
I was taught ever gun is loaded. Even if you check and see its unloaded. Its loaded. Kinda hard to explain to my son. But video's like this help. I still freak out having to pull the trigger on my Glock to break it down. Hate it with a passion. Love my Glock. So its just a part of owning one.