Robert Krulwich

Poor Johannes Kepler. One of the greatest astronomers ever, the man who figured out the laws of planetary motion, a genius, scholar and mathematician — in 1611, he needed a wife. The previous Mrs. Kepler had died of Hungarian spotted fever, so, with kids to raise and a household to manage, he decided to line up some candidates — but it wasn't going very well.

What's the biggest living thing on Earth? I can think of two. I'm not sure which is biggest, but neither of them is a blue whale. These are weirder. Much, much weirder.

One is a tree. The other eats trees.

This is the tree.

Look at this guy.

He is half-smiley, half-frowny. I drew the mouth carefully to make it equal parts sad and happy.

But when you look at him — take him in whole — would you say he's having a good day or a bad day?

Most people would say: good day. He seems a little more smiley than not.

That's because, says science writer Sam Kean, when we look at somebody, the left side of that person's face is more emotionally powerful and "determines the overall emotional tenor."

They don't have eyes. Or ears. Or what we would call a nervous system. But plants can talk. And they listen. Let me show you how.

First, we'll need a plant eater. This one's perfect: It's an aphid, a hungry little critter who loves to munch on fresh, green leaves ...

Next, we arrange lunch. We choose a bunch of young, healthy bean plants with lots of broad, green leaves ...

The U.S. and Canada may be as lovey-dovey as two neighbors can get, but according to this charming video history by CGP Grey, both countries agreed to tuck themselves a little bit in, 10 feet back for America, 10 feet back for Canada, creating a corridor of open, surveillable, clear space between them.