Why do we say 'um', 'er', or 'ah' when we hesitate in speaking?

The Register has a smart sounding chap writing for it these days, explaining the mysteries of life. First up, the age old question of why we say things like ’um’, ’er’ and ’ah’ when we speak. Not everyone says "um", "er" or "ah" when they hesitate while speaking. It depends upon the language.

For example, speakers of Mandarin Chinese often say"zhege" which roughly translates as "this". In English we say "um", "er", "ah", or other vocalisations for reasons that linguists are not entirely sure about. "Um", "er", and "ah" contain what linguists call "neutral vowel sounds" making them among the easiest sounds to make.

Read more (The Register)