What Happened to the Cow’s Front Teeth
Cattle look like they have lost some of their teeth．But the teeth aren’t ceallylost．Cows just don’t have any upper front teeth．Instead，their gums form a hard pad．The lower teeth press against this pad when the cow tears off grass to eat．The cow then chews its food using its strong back teeth．
牛的上门牙怎么啦
牛看上去好像掉了一些牙。然而，实际上并非如此。牛是没有上门牙的，而是有一种坚硬的齿龈。当牛吃草时，先用下门牙和上齿龈咬紧来扯草，然后，再用其坚硬的后牙嚼食。
Why Do Birds Take Dust Baths
Taking baths in the dust may help birds get rid of insect pests that find their way under the feathers．The powdery dust may also help to smooth the feathers and keep them in good condition for flying．After dusting，a bird combs its bill over the feathers to make them lie smoothly．
为什么鸟用沙土洗澡
鸟在沙土里洗澡可以帮助它除去寄生在羽毛中的害虫。粉状沙尘还可以使鸟的羽毛变得光滑，并保持良好的状态，以利于飞行。用沙土洗完澡后，鸟用其尖嘴梳理身上的羽毛，使它整齐光滑。
Why Do Chickens Eat Dirt
Chickens swallow sand and grit to aid in digesting the hard grain they eat．Since chickens have no teeth，they must swallow their food whole．The food goes into a part of the chicken’s stomach called a gizzard．There，strong muscles churn the food and sand together．The sand helps to grind up the grain so the chicken can digest it better．
为什么鸡要吃沙砾
鸡吞食沙砾，是为了帮助消化所吃的坚硬谷物。因为鸡没有牙齿，所以吃东西只好把整个食物吞下去。鸡吃下的食物，进入鸡胃的一个组成部分即沙囊。在那里食物和沙砾混在一起，被强健的肌肉剧烈地搅拌着。沙砾帮助磨碎谷物，从而使鸡能更好地消化它。
Why Does a Bee Die After It Stings
A honeybee’s stinger is covered with pointy barbs．When the bee stings，the barbed stingers ticks in the victim’s flesh so tightly that the bee cannot pull it out．It must tear itself away，leaving the stinger behind．After losing its stinger，the bee dies．
为什么蜜蜂螫人后就会死掉
蜜蜂的螫针上有一些很尖的倒钩。蜜蜂螫人时，带倒钩的螫针，牢牢地扎在人的肌肉里而不能拔出。因此，蜜蜂只得留下螫针，撕尾离去。失掉了身上的螫针以后，蜜蜂很快就会死去。
What Does the Electric Eel UseIts Electricity For
The electric eel uses its electricity to catch food and to protect itself from enemies．The electricity is generated by batterylike cells in the eel’s body．An electric eel can produce as much as 800volts！This can light a lamp or stun an alligator．The shock a fish gets when it touches the eel knocks it out and makes it easy eating for the eel．
电鳗身上的电有什么用处
电鳗用其身上的电捕捉食物和防御敌人的进攻。它身上的电是由一种电池似的细胞所产生的。一条电鳗能够产生高达800伏的电。这可以点燃一支电灯泡或击昏一条鳄鱼。别的鱼一旦接触电鳗就会触电昏迷，从而成为电鳗随手可得的食物。
Why Are Moths Attracted to a Light
A moth is not really attracted to a light．The moth uses the moon as a beacon to guide it as it flies about at night．But your nearby porch light fools it．The unwitting moth tries to use its bright light to navigate with instead of the moon，and is guided into the light．
蛾为什么扑灯
飞蛾并不是真的扑灯。当蛾在晚上飞翔时，总是把月亮当作引导自己的指向标。但是，你附近门廊的灯光愚弄了它。它误把灯光当作月亮来导向，于是就不知不觉地向灯光扑去。
Why Do Moths Eat Wool
It isn’t the adult moth that makes the moth holes in our woolens．The adult never eats．It is while the moth is in its caterpillar stage that it does this damage．The adult lays its tiny eggs on furs and woolens．Then it dies．The caterpillar hatch and feed on the material，causing serious damage．
为什么蛾虫蛀毛料
在我们毛料上蛀洞的并不是成熟的蛾。成熟的蛾绝对不蛀毛料。只有当蛾处于毛虫阶段时，才会造成这种损害。成熟的蛾在皮料和毛料上排出小卵，然后就死去。毛虫孵化出来后就以这种皮毛作饲料，从而引起衣料严重损坏。
Why Does an Octopus Squirt Its Ink
An octopus squirts its ink to escape enemies．It stores its inky fluid in a special sac inside its body．When a shark or other enemy comes near，the octopus squirts its ink．The inky fluid forms a dark cloud in the water that dulls the enemy’s sense of smell and helps hide the octopus long enough for it to escape.
章鱼为什么喷墨汁
章鱼喷出墨汁是为了逃避它的敌人。它那墨汁一样的液体贮藏在体内的一个特殊的液囊里。当鲨鱼或其他敌人逼近时，章鱼就喷出它的墨汁。墨汁一样的液体在水中形成一片黑团，它使敌人的嗅觉变得迟钝，并
把章鱼遮蔽起来，从而使它有足够的时间逃掉。
How Does a Chameleon Change Its Colour
The American chameleon can change its colour from green to brown．This little lizard has special colour cells in its skin．When these cells change size and shape，we see a change in the colour of the chameleon．One thing that makes the colour cells show a different colour is the chameleon’s mood．Other things are light and whether it is hot or cold．The chameleon is not always the same colour as the stuff it is sitting on．
变色龙是怎样变换它的颜色的
美洲的变色龙能把身上的颜色由绿色变为棕色。这种小蜥蜴的皮肤里有一种特殊的色细胞。当这些细胞改变其大小和形状时，我们就会看到变色龙颜色的变化。能使色细胞变换不同颜色的一个因素是变色龙的情绪。另外一些因素是光线以及天气的冷热。变色龙的颜色与它所栖身的地方的颜色并非总是保持一致．
How Does a Flamingo Get Its Pink Colour
The flamingo’s pink colour is caused by pigments called carotenoids，which come from the food it eats．To preserve their bright pink colour，flamingo in zoos are fed a diet of carrot juice，beets，paprika，and raw shrimp．Without the proper food，the big bird’s fine feathers fade to drab offwhite．
火烈鸟身上的粉红色是怎样产生的
火烈鸟身上的粉红色是由叫做胡萝卜素的色素所产生的，这种胡萝卜素来自火烈鸟所吃的食物中。为保持其鲜艳的粉红色，动物园里的火烈鸟要喂给特种饲料：胡萝卜素汁、甜菜、红辣椒和生虾。没有这些合适的食物，这种大鸟美丽的羽毛就会褪色成黄褐色至灰白色。
How Does a Rattlesnake Rattle
It’s easy to tell a rattlesnake-by the rattle at the end of its tail．The Rattle is a series of cupshaped rings that fit loosely together．When the snake is alarmed its tail vibrates．The rings strike together and make a sharp buzzing sound．By making its rattling noise，the snake is able to warn away bigger animals that might harm it．A new ring is added to the rattle each time the rattlesnake sheds its skin．
响尾蛇是怎样发出响声的
认出响尾蛇是很容易的，因为其尾巴末端有响环。响尾蛇的尾部是一些松弛地连接在一起的杯形环。当响尾蛇受到惊吓时，它的尾部就摆动起来。杯形环就互相碰撞，从而发出尖锐的响声。响尾蛇发出这种响声，能够把一些较大的、可能会伤害它的动物吓跑。响尾蛇每蜕一次皮，就会增加一个新的杯形环。
Why Do Birds Migrate
Although the ice and snow of winter make it hard for some birds to find food，birds do not migrate just to find food．It is likely that the length of the day helps create the need to travel．Probably，birds fly northward in the spring because the longer summer days allow them to gather the extra food needed to raise their young．Once the nesting season is over，many birds return south，long before the arrival of winter．
为什么鸟要定期移栖
虽然寒冬的冰雪使得一些鸟难以寻找到食物，但鸟不仅仅是为寻找食物而移栖的。可能是白天的长短，促使鸟类作必要的旅行。通常鸟类在春天向北飞去是因为那里夏天的白天较长，这样可以使它们能去捕捉更多的食物以哺育它们的后代。一旦巢居季节结束，许多鸟远在冬天到来之前就飞回南方去了。
How Do Bees Make Their Beeswax