英语时差：墨西哥跳豆为什么会跳跃（上）

On the table in front of you, it looks like a small, dried bean. Pick it up. To your surprise, it starts to wiggle, shifting around nervously in your palm. Suddenly, it squirms back onto the table again. We’ve all heard stories about Mexican jumping beans. What are they, and how do they do that remarkable trick? Actually, jumping beans aren’t beans at all. They are the seed pods of a certain shrub that grows in the rocky desert areas of northern Mexico and the American southwest. These seed pods can’t jump by themselves. What makes a jumping bean so jumpy is the larva of a small grey moth that has burrowed inside the seed pod and eaten the seed.