I don’t recall much of my high school chemistry classes back in Sri Lanka. Our teacher was a nice old man who enjoyed telling us the history of chemistry and stories about the chemists of long ago rather than about modern chemistry. But he was a believer in experimentation and demonstrations and one that I remember was when he would cut a small piece of solid sodium and drop it into a beaker. It was fun to see the piece foaming and rushing around the container.
Solid sodium is highly dangerous and can cause severe burns so he would not let us handle it but only do this himself with us watching. I am not sure whether with our increased concern for safety in science classes, this kind of demonstration would even be allowed these days, just as the way we would play with liquid mercury would now horrify people.
But some people have managed to get a large chuck of sodium and recorded what happens when they throw it into a pond, creating essentially a scaled-up version of that demonstration.