49 Knock! Knock!

Knock on wood. Woodpeckers do just that. This bird is an amazing creature: it pecks so hard and fast that its head looks like a blur. The woodpecker knocks on dead wood, looking for insects to eat. Its chisel-like beak chips away bark and decayed wood, and the violent tapping disturbs insects hidden in the tree’s cavities. When the woodpecker reaches the insects’ home, it spears its dinner with a barbed and sticky tongue.

The woodpecker pecks at a speed of 1,300 miles per hour. At this speed, the impact of the bird’s beak hitting the wood is almost like that of a supersonic jet smashing into a mountain. Each peck takes just a thousandth of a second. The movement is quicker than the human eye can follow. Incredibly, the bird’s cherry-sized brain is never injured from all this furious smashing.

There is a secret to the woodpecker’s ability to withstand the great impact of its pecking. The head and beak move only in a straight line. They are so well coordinated that there’s little in the woodpecker’s neck muscles. This spreads the shock evenly, though the bird’s body and into the tree trunk. Pecking at even a slight angle would kill the woodpecker. Design experts are using this bird as a model. They hope to come up with a crash helmet that will better protect people’s head from injuries.

49 咚咚！咚咚！

敲木头。啄木鸟就是这么做的。这种鸟是一种神奇的生物：它啄击的力度大且速度快，头部看起来一片模糊。啄木鸟敲击枯木，寻找昆虫作为食物。它那凿子般的喙啄掉树皮和腐烂的木头，猛烈的敲击声惊扰了藏在树洞里的昆虫。当啄木鸟到达昆虫的巢穴时，它用带刺且黏的舌头刺穿猎物作为晚餐。

啄木鸟的啄击速度达到每小时1300英里。在这个速度下，鸟喙撞击木头的冲击力几乎就像超音速喷气式飞机撞击山脉一样。每次啄击仅耗时千分之一秒，其动作之快人类的眼睛都难以跟上。令人难以置信的是，这只鸟樱桃大小的大脑从未因这种猛烈的撞击而受伤。

啄木鸟能够承受其啄击的巨大冲击力是有秘诀的。头部和喙只沿直线移动，它们的协调性非常好，啄木鸟的颈部肌肉几乎不会受到影响。这样可以均匀地分散冲击力，尽管鸟的身体会随之进入树干。即使以微小的角度啄击也会杀死啄木鸟。设计专家正以这种鸟为模型，希望设计出一种更能保护人们头部免受伤害的防撞头盔。