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Dear Dr. Universe: Why are animals symmetrical?

Dear Theo,

That’s an excellent observation. If we drew an imaginary line straight down the middle of the human body, it would look pretty similar on each side.

We see this kind of symmetry in lots of animals, from cats and birds to worms and frogs. In fact, about 99 percent of animals have bilateral or two-sided symmetry, says my friend Erica Crespi.

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How does a string of lights work?

Just the other day I was taking down a string of lights from my lab, when I discovered the bulbs were burnt out. I visited my friend Aaron Crandall, an engineer at Washington State University, to see if I might get them working again.

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Why do animals live in groups?

Fish swim in big schools. Baby ducks waddle in a straight line. Ants and bees divide up labor. The world is full of animals that live in groups and they do it for a few different reasons.

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How is glass made?

We can make glass in factories and we can find it in nature. Some volcanoes make glass. When they spew out lava, it often cools into obsidian, a black glass. Glass can also form on sandy beaches. Small tubes with smooth glass on the inside may appear after super-hot lightning strikes the sand.

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Do all animals pass gas?

If you’ve ever been near a cat or dog when they tooted, the smell might have sent you running right out of the room. A lot of animals pass gas. But believe it or not, some animals do not.

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