Talking to animals, including baby human animals, is a waste of time. They don't know what you're saying. But there has been an experiment that proves certain animals they do know what language you're saying it in.
Scientists at the University of Barcelona have figured out that animals can distinguish between different human languages. How did they do this? They started slow, with cotton-top tamarin monkeys and human infants (unfortunately not in the same room at the same time). The procedure of the experiment was simple: the monkey or infant (oh, how I wish it had been both) sat in a room with a speaker. The speaker played either Japanese or Dutch sentences while a team of scientists gauged subject's level of interest in the sound. Apparently when infants are interested in something, they ramp up the intensity with which they suck on their pacifier. Monkeys, who have better neck control than human infants and are rarely provided with pacifiers, just turn towards the speaker. After a few minutes, the sounds no longer held either subject's interest, and they showed signs of boredom. When the language on the speaker changed, from Japanese to Dutch or Dutch to Japanese, round went the head again. Both human babies and monkeys knew the difference in the melody of speech.
The scientists took it one step further when they decided to train rats. The experiment in this case was more elaborate, as rats could be motivated by the gifting and withholding of food. (People tend to frown on that sort of thing with human infants.) The rats were separated into two groups. If the "Japanese" rats pushed a lever while four specifically-selected Japanese sentences played on a speaker, they got food, but they got nothing if they pressed a lever while four Dutch sentences were being played. The "Dutch" rats got food for lever-pushing during four Dutch sentences, but not during Japanese sentences.
The rats were quickly trained. They were then played new sentences, sentences that they'd never heard before, either in Dutch or in Japanese. The rats only responded to "their" languages. They never understood the words, and they couldn't understand the new sentences, but they had a feeling for the sound and rhythm of their languages. So when you go through a foreign city and see a rat don't scream and yell. If you do, the rat will be able to tell that you're a tourist.
Then they get mean.
Top Image: Harald Hoyer.