科學家表示，響尾蛇已經進化出一種聰明的方法，讓人類誤以為危險比他們想象的更近。

The sibilant sound of the rattlesnake's tail has long been a cinematic cliche.

響尾蛇尾巴發出的嘶嘶聲早已是大銀幕上的常用套路。

That tell-tale rattle is made by the rapid shaking together of hard rings of keratin at the tip of the creature's tail. Keratin is the same protein that makes up our fingernails and hair.

這種具有警示作用的咔咔聲是由該生物尾部末端堅硬的角蛋白環一齊快速搖動時產生的。這種角蛋白與構成我們指甲和頭發的是同一種蛋白質。

In this study, the scientists found a distinctive switch to a higher frequency as objects move closer to a western diamondback snake.

在這項研究中，科學家發現，當有物體接近西部菱斑響尾蛇時，蛇尾發出的響動聲會明顯切換到更高的頻率。

When human test subjects were exposed to this change in sound, they believed they were almost on top the snake, when in reality they were safely distant.

當人類受試者暴露在這種聲音變化中時，雖然其實他們離蛇還有一段安全距離，但他們會以為自己幾乎就站在蛇的上方。

The scientists believe rattlesnakes evolved this trait because it helped them to avoid being stepped on by humans.

科學家認為，響尾蛇進化出這種特性是因為這樣可以幫助自己避免被人類踩到。

Despite this clever sound trick, hikers and walkers in the United States often find themselves in unwanted contact with these reptiles.

盡管響尾蛇有這種精明的聲音花招，美國的徒步旅行者和步行者還是經常會意外遭遇到這些爬行動物。

Rattlesnakes are responsible for the majority of the 8,000 people bitten in the US every year.

美國每年有8000人被蛇咬，其中大部分的罪魁禍首都是響尾蛇。

詞匯表

sibilant 嘶嘶作響的，此文指響尾蛇尾部搖動時發出的聲音
cliche 老套的內容
rattle 咔咔聲，短促尖厲的撞擊聲
keratin 角蛋白
frequency 頻率
exposed 暴露（在特定環境中）的
distant 遠處的
evolved 進化出了
reptiles 爬行動物

閱讀理解：請在讀完上文后，回答下列問題。

1. How do rattlesnakes make their sound?

2. In what way do rattlesnakes change the sound they make as objects get nearer?

3. What types of people in the US often encounter rattlesnakes?

4. How many people are bitten by snakes in the US each year?

答案  

1. How do rattlesnakes make their sound?
Rattlesnakes make their sound through the rapid shaking together of hard rings of keratin at the tip of the creature's tail.

2. In what way do rattlesnakes change the sound they make as objects get nearer?
Scientists found a distinctive switch to a higher frequency as objects move closer to a western diamondback snake.

3. What types of people in the US often encounter rattlesnakes?
Hikers and walkers in the US often find themselves in unwanted contact with these reptiles.

4. How many people are bitten by snakes in the US each year?
Around 8,000 people are bitten in the US every year.