That's because chocolate contains caffeine and a chemical called theobromine.

这是因为巧克力含有咖啡因和一种叫做可可化学物质。

Smaller dogs will have more severe reactions, and the amount of caffeine and theobromine in chocolate varies.

体型较小狗会有更严重反应，巧克力中咖啡因和可可含也各不相同。

They process theobromine a lot more slowly, so it can easily build up and cause those dangerous effects.

他们代谢可可度很慢，所以可可很容易在体内累积并造成危害。

Your average adult human would need to eat about 8 kilograms of dark chocolate to get a lethal dose of theobromine.

一般成年人需要吃掉大约8公斤黑巧克力，才会摄入以致死可可。

Early studies suggest small doses of very dark chocolate, rich in antioxidants, theobromine and caffeine may make us happier, healthier and less stressed.

早期研究曾指出一小块黑巧克力里含有丰富抗氧化物、可可硷和咖啡因可使人心情愉悦、放松心情以及更健康。

Both molecules are dangerous for dogs but chocolate contains a lot more theobromine than it does caffeine so it's the molecule to watch out for.

咖啡因以及可可对于狗来说都相当危险，但巧克力中含有可可成分相比咖啡因还要来得多，所以要注意是这两种成分。

Also like caffeine, theobromine makes our heart pump faster, our blood vessels dilate, and some of our muscles get more energy, which sounds great!

就像咖啡因，可可也会促使我们心跳加快，血管扩张，以及让部分肌肉得到更多能，这听起来很棒。

Whatever the reason, the same amount of theobromine stays in pets' bodies much longer, giving it more time to pile up and cause harm.

无论原因如何，等可可会停留在宠物身体里更久时间，使得可可更容易累积并造成伤害。

Like caffeine, theobromine is a type of alkaloid, which is a huge class of molecules that generally contain rings with at least one nitrogen atom in them, and alkaloids often have physiological effects on humans and other animals.

和咖啡因一样，可可属于生物一种，生物是相当大一类分子，一般来说它环中会包含至少一个氮原子，生物通常会使人类及其他动物产生生理作用。

Sweeter chocolates have less theobromine, so the lethal dose is higher; about 5 kilograms of milk chocolate for dogs and about a third of a kilogram for cats, but they'd be sick long before eating that much.

较甜巧克力所含可可较少，所以以致死相对会较高，吃下约 5 公斤牛奶巧克力会导致狗狗死亡，猫则是要吃下约 300 多公克，不过他们在吃下那么多分之前就会先感到恶心了。

It's hard to know exactly why we evolved to be better at digesting theobromine, but it might be because alkaloids mostly come from plants, and our ancestors ate a lot more plants than early cats or dogs did.

我们很难确切了解为什么我们身体会进化成能较容易消化可可，有可能是因为生物大部分都来自植物，而我们祖先吃植物比以前猫和狗所吃植物多很多。