I was thinking about helium

Helium is the second element in the periodic chart of chemical elements. Sixth is carbon, and eighth is oxygen. Helium has an atomic weight of around 4, carbon's weight is around 12 and oxygen's weight is around 16. So oxygen weighs about 4 times as much as helium.

You can put a bunch of pencil lead in a bag and toss the bag on a scale and weigh it. How did they figure out that helium weighs "4"? Picture a scientist filling a bag with helium and putting it on a scale and watching the bag go to the ceiling, and then repeating this. (A senior scientist then ties the bag to the junior scientist's wrist with a string.)

There is probably some place that helium exists naturally, like in some part of the rain forest. It seeps out of certain logs or large bugs. And there are certainly natives in that area. Wouldn't those natives have a great time, I thought. They'd never have a serious conversation. Tony the Elder would try to bring up some serious matter with Frank, like how he's being kept awake by Frank's kids beating on logs late into the night, but then they'd both burst into laughter because Tony the Elder sounds like a chipmunk and they'd be wiping their laughter tears from their eyes with the backs of their hands and then go back to blow-darting tree snakes. But then I realized that that's what they grew up with, and what you grow up with is often what feels normal. They would have always sounded like chipmunks and it would not have occurred to them that they might sound different from other humans. So, they wouldn't laugh because of the helium.

What would be interesting is taking these natives out of their part of the forest, say, to meet another tribe. (The first challenge would be for the host who arranges the trip. As desperately as the host wants to talk the natives into the idea of traveling for this social experiment, he can't get a complete sentence out because he's laughing at himself sounding like a chipmunk.) There would be some point in the travels at which the natives would first hear each other talk with low voices. "Tony the Elder, you sound like a rotted log!" they'd laugh. (They wouldn't say he sounded like a tiger or other big animal because in their part of the rain forest those animals would also sound like chipmunks [and, come to think of it, I don't know what chipmunks would sound like there]). And they'd laugh again when they heard the neighboring natives speak in low voices. The neighbors would be totally serious, but the helium natives would just not be able to keep a straight face. Trying to suppress your laugher in a serious setting, when you know your buddy Frank has the same silly thought--that just leads to outbursts and snorts that can't be contained. And when they got back home and tried to imitate low voices to their families, they just couldn't describe it well enough, so it wouldn't be that funny.

That's what I was thinking about helium.