With half as many neurons in their cerebral cortex as cats—and half the attitude, some would say—dogs are often taken to be the less intelligent domestic partner. While dogs drink out of the toilet, slavishly follow their master and need a chaperone to relieve themselves, cats hunt self-sufficiently and survey their empire with a regal gaze.

But cats beware. Research in recent years has finally revealed the genius of dogs.

Like other language-trained animals—dolphins, parrots, bonobos—dogs can learn to respond to hundreds of spoken signals associated with different objects. What sets dogs apart is how they learn these words.

If you show a child a red block and a green block, and then ask for the chromium block, not the red block, most children will give you the green block, despite not knowing that the word "chromium" can refer to a shade of green. Children infer the name of the object. They know that you can't be referring to the red block.

In 2004, Juliane Kaminski from Britain's University of Portsmouth and her colleagues published the results of a similar experiment with a dog called Rico who knew the names of hundreds of objects.

Dr. Kaminski showed Rico an object that he had never seen before, along with seven other toys that he knew by name. Then she asked Rico to fetch a toy using a word that was new to him, like "Sigfried." Just like human tots with the word "chromium," Rico was immediately able to infer that "Sigfried" referred to the new toy. Since the report on Rico, several other dogs have also been shown to make inferences this way. Dogs are the only animals that have demonstrated this humanlike ability.

Read more at The Wall Street Journal.