Science

Take a close look at a house cat's eyes and you'll see pupils that look like vertical slits. But a tiger has round pupils — like humans do. And the eyes of other animals, like goats and horses, have slits that are horizontal.

Scientists have now done the first comprehensive study of these three kinds of pupils. The shape of the animal's pupil, it turns out, is closely related to the animal's size and whether it's a predator or prey.

Men who work out may be using legal over-the-counter supplements to the point that it's harming their emotional or physiological health, according to a recent study.

#NPRreads is a weekly feature on Twitter and on The Two-Way. The premise is simple: Correspondents, editors and producers throughout our newsroom share pieces that have kept them reading. They share tidbits using the #NPRreads hashtag — and on Fridays, we highlight some of the best stories.

This week, we bring you three items.

From NPR's South America correspondent, Lourdes Garcia-Navarro:

When I was a kid, I noticed that sometimes fear and anticipation felt the same way.

I'd get butterflies, a kind of queasiness in the stomach. To figure out what I was feeling, I came to realize, what was needed was not introspection, but attention to the context.

Some days, the french fries are just irresistible. You know it's not the best thing to put in your body, but did that salad really stand a chance after the smell of fried garlic, Parmesan and thyme on crisp potato wedges wafted over to you?

It goes by many names: Delhi belly. Montezuma's revenge. The Aztec two-step. But doctors use one not-so-glamorous term: traveler's diarrhea.

If you're visiting a place this summer with less than ideal sewage disposal — maybe a resort in Mexico or a village in Rajasthan — chances are your GI tract will give you trouble at least once ... maybe twice ... maybe continuously.

When I interviewed mathematician Eugenia Cheng for an upcoming episode of The Sporkful podcast, she sliced a bagel along a Mobius strip.

A Mobius strip, in case you're not familiar, is a surface with only one side. You can make one by taking a strip of paper, twisting one end halfway around, and taping it to the other end. Like this:

Humpback whales don't just sing songs — they compose with the whales around them, singing a song that evolves over time. Scientists didn't know that until they started recording whale sounds in the 1960s and spent years listening. The evolution of this "culture of listening" among researchers is the focus of Morning Edition's weekly summer series, Close Listening: Decoding Nature Through Sound.

The name Hiroshima is so tied to the atomic bomb that it's hard to imagine there were other possible targets.

But in early 1945, the U.S. was still months away from building its first bomb and certainly didn't know what to hit.

"Should it be a city? Should it be a military installation? Should you be just displaying the bomb, without killing anybody?" These are questions that were yet to be decided, says Alex Wellerstein, a historian at the Stevens Institute of Technology.

The idea that our oceans teem with cultural animals — and have for millions of years — is the central conclusion of a new book by two whale scientists. And it's a convincing one.

Whales and dolphins, as they forage for food and interact with each other in their social units, may learn specific ways of doing things from their mothers or their pod mates.