We've all experienced it: that uncomfortable pressure in your stomach that suddenly turns into surprisingly intense pain. But if intestinal gas is a completely normal part of digestion, why can it hurt so much?

In this episode of Why Stuff Happens, we explore what's actually happening inside your digestive system when gas builds up. Discover where intestinal gas comes from, why stretching the intestines can trigger pain, what people really mean by "trapped gas," and why your brain sometimes has trouble figuring out exactly where that discomfort is coming from.

We'll also look at why the same amount of gas can barely bother one person while leaving someone else miserable, how gut bacteria help produce gas in the first place, and why feeling bloated doesn't always mean your body actually contains an unusually large amount of gas.

It turns out the gas itself isn't necessarily the painful part. The real story involves pressure, stretching, muscles, nerves, and a digestive system that can be surprisingly dramatic.

So the next time your stomach starts complaining after dinner, you'll know a little more about why stuff happens.

Cats purr when they're happy… right?

Not always.

In this episode of Why Stuff Happens, we explore the surprisingly complicated science behind one of the most familiar sounds in the animal world. How does a cat actually produce a purr? Why can cats purr while breathing both in and out? And why do some cats purr when they're frightened, stressed, injured, or even at the veterinarian?

We'll also look at the fascinating relationship between kittens and their mothers, the unusual "solicitation purr" some cats may use to get our attention, and the popular claim that purring might have healing properties.

The deeper scientists look into purring, the more interesting the story becomes. It turns out that a cat's quiet little rumble may communicate much more than simply, "I'm happy."

So settle in, get curious, and discover why cats purr.