Acoustic cues are the hundreds of small variations in word pronunciation that create shades of meaning, accents, and many other small elements of human language. For instance, this can be how long a vowel sound is held in the pronunciation of a word (i.e. cot and caught). If you compare these words you will find that the vowel sound in 'caught' is held just a fraction longer than it is in 'cot.' This is just one of the small "cues" that separate homonyms from each other in English. Many other languages (i.e Spanish, French, and many others) also rely heavily on inflections to differentiate words that are similar to one another. If you have ever studied foreign languages you will probably ave experienced how inflected differences work.