Watch this electric eel slay an alligator

The electric eel is actually not an eel at all, but a type of fish called a knifefish, more commonly related to the catfish than anything else.

The fish has three internal organs that produce electricity, the main organ, the Hunter's organ, and the Sach's organ, making up 4/5 of its body.  It can discharge low and high voltage electricity.

"When the eel locates its prey, the brain sends a signal through the nervous system to the electrolytes.  This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electric potential difference."

Here, the fish slays an alligator that is attempting to eat it

Though it only produces a small burst of electricity (860 volts and 1 amp for two seconds at a time), it is certainly enough to kill small animals.  A human adult would likely survive the shock.

Watch them eat

Researchers at Yale University and the National Institute of Standards and Technology say that artificial cells could be built that not only replicate the electrical behavior of electric eel cells, but also improve on them.

Collectors have sought electric eels for ages and found the best way to capture them is to provoke them to discharge all of their electricity, then reach for them.  Life in captivity for an electric eel is mostly relegated to zoos and aquariums.