别以为“天上掉青蛙”这样的怪事只发生在《出埃及记》里面的摩西身上，要是哪天早晨你睡醒，发现一夜之间天上“掉下”了满地青蛙，那才麻烦呢。
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The plague of frogs mentioned in Exodus began in Egypt.
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Can it really rain frogs?
It's hard to get a good mental picture（使形象化；想像）of frog inundation that doesn't have Moses standing off in the distance. The biblical image of a slimy, surprising mass is tough to avoid. However, there's actually a pretty simple explanation for the whole thing: It involves whirlwinds and low-weight creatures.
Frogs can weigh as little as a few ounces. But even the heavier ones are no match for a watery tornado, or a waterspout, as it's called when a whirlwind picks up water. The series of events that can lead to frog rain go something like this:
A small tornado forms over a body of water. This type of tornado is called a waterspout, and it's usually sparked by the high-pressure system preceding a severe thunderstorm.
As with a land-based tornado, the center of the waterspout is a low-pressure tunnel within a high-pressure cone. This is why it picks up the relatively low-weight items in its path -- cows, trailer homes and cars get sucked up into the vacuum of the vortex. But since a waterspout is over water and not land, it's not automobiles that end up caught in its swirling winds: it's water and sea creatures.
The waterspout sucks up the lower-weight items in the body of water as it moves across it. Frogs are fairly lightweight. They end up in the vortex, which continues to move across the water with the high-pressure storm clouds. When a particularly powerful storm hits land, the waterspout might go with it.
A sudden downpour of frogs is one of the most bizarre weather events.
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When the storm hits land, it loses some of its energy and slows down. The pressure drops. Eventually, the clouds release the water they're carrying. As the rain falls, the vortex eventually loses all the pressure that's keeping it going, and it releases whatever it has picked up in its travels. Sometimes, this cargo includes frogs.
The end result is frog rain. Sometimes it's a few dozen frogs -- or a couple hundred or even thousands. And usually, it's not just frogs. Frogs get top billing because of their role in Exodus, but waterspouts can carry all sorts of items. The plague of frogs mentioned in Exodus began in Egypt. A sudden downpour of frogs is one of the most bizarre weather events.
（来源：howstuffworks网站 实习生许雅宁 英语点津Yvonne编辑）
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