True to their name, boa constrictors squeeze the life out of their prey. But how does a boa know it's snuffed out a rat? The snake listens for a heartbeat. When it stops, that's the cue to let go, according to a study in the journal Biology Letters.
蟒蛇可是名副其实的猎物杀手。但蟒蛇是怎么知道它们已经成功杀死了一只老鼠？原来，蟒蛇会听老鼠的心跳。当老鼠心跳停止了，它们就会放松紧缠着老鼠的身体。这项研究发表在《生物学快报》杂志上。

Researchers outfitted rat cadavers with artificial beating hearts. They used dead rats to control for other signs of passing, like muscle spasms. Then they warmed up the rats, set the hearts pumping, and dangled them in front of hungry boas.
研究人员人工控制死鼠的心跳。他们用人为控制的死鼠肌肉痉挛来表现老鼠已经死亡。然后，他们把死鼠的身体弄热，安装上人造心脏泵，再把死鼠放在饥饿的蟒蛇面前。

The snakes attacked. And as long as that rat heart kept thumping, the boas kept tightening their coils and applying bursts of pressure, sometimes for more than 20 minutes. But as soon as scientists killed the heartbeat, the boas loosened up.
蟒蛇开始攻击了。只要老鼠的心脏还在不停跳动，蟒蛇就不断收紧身体并一阵阵地用力缠绕，有时超过20分钟。但是，一旦科学家让死鼠停止心跳，蟒蛇就会松开身体。

Even captive-born boas who'd never hunted live prey paid attention to the pulse—suggesting the behavior is innate. And for good reason. The authors say constriction takes a lot of energy. And it can be dangerous, say, if an enemy strikes while the snake's coiled around its quarry. But by following the telltale heart, boas can keep the pressure on just long enough. Before a relaxing meal.
即使圈养长大的、从来没有猎杀过鲜活猎物的蟒蛇也会注意猎物的心跳——这说明这种行为是与生俱来的。这是可以解释蟒蛇这种行为的很好的理由。作者称，蟒蛇捕猎时的身体收缩会耗费大量的力气。但这样也很危险的，比如说，如果在蟒蛇盘绕在猎物身上的时候，天敌突然袭击。但通过倾听猎物心跳的方式，蟒蛇可以给猎物施加足够的扼杀力，然后轻松享用美餐。