Have you ever tried to have a conversation with a baby? It's all 'goo' this and 'gah' that - not particularly fulfilling. You might think that babies don't understand anything that's being said to them, which is, in a sense, true. Babies don't comprehend the words that are being said to them, but they do possess an innate ability to understand the sound of the human voice and to discriminate between parts of language. Experiments done on babies as young as a few days old have shown they recognize phonemes, which are the smallest units of speech that differentiate one word from another. A baby can tell the difference between the words 'mom' and 'mop,' for instance, without actually knowing what the two words mean.