Imagine testing glass by throwing chickens at it? Sometimes fast moving airplanes fly through flocks of birds. If the birds hit the windshield of a plane, the glass could shatter and cause a crash. Airplane manufacturers have made a chicken cannon that fires rubber chickens at glass windshields. If the windshield doesn't break when the rubber chicken hits it, the designers know that the glass can withstand the force of a real crash.

Most people think that gorillas are mean, but actually they are shy. It seems that such a huge animal with very large teeth would be aggressive. Hollywood movies help convey this image of the scary, ferocious gorilla. In fact, gorillas only attack if they are provoked. 
This author belives that:

What is the Central Idea of the passage?
What's that humming sound?  Could it be hummingbird, the only bird capable of backward flight?  Hummingbirds have many unique flight habits that distinguish them from other birds.  Most birds flap their wings up and down to fly, but the hummingbird moves its wings forward and backward very rapidly in a figure eight pattern.  This allows the hummingbird to hover in position, fly upside down, and move about very rapidly.  And while other birds have to push off with their feet to begin flying, and work their ways up to their top speeds, the hummingbird can both start flying at maximum speed and stop flying instantaneously.  After you've seen a hummingbird in flight, it's unlikely that you'll mistake them for another bird.