How do popcorn kernels pop? How do salmon know where to return to spawn? How do rabbits change colors? Why does television fry your brain? How do zippers zip stuff? Who was the fastest runner in the world? In this episode, we'll tackle all of these questions!

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• Inside the husk is a tiny little droplet of water surrounded by something called the endosperm. The endosperm is what you're actually eating when you eat popcorn. When you heat up popcorn, the tiny droplet of water gets hot and turns into steam. That steam pushes through the endosperm and turns it kind of soft and that endosperm builds up pressure and explodes through the husk. When it explodes, that soft gelatinous endosperm hits cooler air and it hardens up in whatever shape it has exploded into. So that's why popcorn has all those funny shapes and feels kind of like foam.

• Salmon are born in freshwater, but then spend their lives in saltwater. They return to the freshwater to spawn (lay and fertilize eggs) and die. Some salmon return to any body of freshwater to spawn, but some salmon have special ways of finding their way back to the place they were born. They use a kind of internal compass to head back to the spot. Other fish rely on their sense of smell to find their way back to fresh water.

• Animals that turn white in winter use the length of day as their cue to stop producing pigment in their fur. Their bodies can sense the hours of daylight, and when the daylight starts getting shorter, their hormones will tell the cells to stop producing melatonin. Hormones tell the cells what to do to shut off the production of pigment in the fall and to turn it on again in the spring. It's not because the days and the nights get colder or warmer.

• The fastest runner in the world is Usain Bolt. He's the fastest man who's ever been timed. He's a Jamaican sprinter, and he holds the world record for both the 100 and the 200 meter sprints. He has nine gold medals at the Olympics and 11 world championships. His record for the 100 meter sprint is 9.58 seconds. That is super fast. That's more than 23 miles an hour.

• Want to pop your own popcorn from kernels? Find a big pan with a tight-lid. Pour two tablespoons of cooking oil in the pan. Then add a half a cup of popping corn. Cover the pan and turn the heat to high. In a few minutes the popcorn will start to pop. Turn off the heat. Open the lid when the popcorn stops popping. Enjoy!

How a zipper works

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