Hello Centrino, Those are just words used to indicate certain emotions, they started as gibberish words used intuitively to express certain emotions and by time and use have been coined as words in dictionaries . Aah: indicates : - surprise or amazement : " Aah , that is really beautiful" - joyful pleasure: "Aah, yes i enjoyed it very much" - understanding , expresses understanding: " Aah , now I understand". The word "aah" could be both a noun as in previous examples or a verb " to aah" : "Every one passing by aahed over her new appearance " It means were amazed or surprised. Umm: This noun is used to express doubt or uncertainty : " Umm , I am not sure of it " It is also used to fill a pause when hesitating in speech: " He is kind of umm umm ,I can almost say nice and kind."

It's almost like saying "nege...nege...nege" however, 'uhmmm' and 'ahhh' are called para-language; non-verbal elements which accompanies speech. You're unsure of what to say next or thinking of what to say. 'Ahhh' can also be used to express awknowledgement too. e.g 'Uhmmm' "What would you like?" "Uhmmm I'll have that uhmmm.... big mac with medium coke please" e.g 'Ahhh' "....so if you buy this burger with your medium coke, you get a free apple pie" "Ah! I get it, I'll get that then please." "What would you like?" "Nege....nege... medium coke and big mac please"