So... I was thinking a few days ago about orthography. I was thinking that it is supposedly really difficult for native Hawaiian speakers and native Japanese speakers and native Chinese speakers (and probably others) to pronounce words which have more than one consonant sound in a row. And, native English speakers often have much trouble with Eastern European names that are "just about all consonants". However, it's not inherently difficult for any native speakers of any languages (to my knowledge) to pronounce words with multiple vowel sounds in a row.
In fact, the Japanese phonetic alphabets have five vowels, a whole slew of sounds that are all 'consonant-vowel', and then an /n/ or /m/ sound that can never start a word.
What makes consonants and vowels so different?
My initial thought was that you can stretch vowels but not consonants. That's just not true. I can hold an /f/, /h/, and /s/ just fine. I may even be able to hold a /b/ or /w/ though those might be more like /be/ and /wa/ which are really holding the vowel.
I thought it might be the rounding of mouth with vowels. But, for long vowel sounds, I'm pretty hard pressed to think my mouth is any rounder than it is with /h/ or /d/.