Voice

Each human has a unique "Voice". Everyone has a different set of noises that they can emulate using vibrations. These are then sorted into categories like laughter, words, cries and so on and so forth. Although we would like to believe that we can distinguish voices splendidly, it is only possible for people you meet regularly. It is almost impossible to connect one type of voice like laughter to another like vowels (produced by the same person), although it is relatively simple to recognize the same voice reproduced (two laughters). Everyone has their own vocal cords, except maybe twins however theirs will most likely develop a different pitch compared to the other one. Even if it was somehow magically the same, they most definitely wouldn't have the same exact accent, or laugh.