(urth) Wolfe's brilliance or my denseness?

[Lee Berman]

>Jeff Wilson- How do we know Casdoe is a Kazz, then? I thought it was Kass-Dough.
 
Well, regional and individual dialects differ. But "Z" is the voiced analog of the
unvoiced "S" sound. "D" is voiced.
 
It is a general linguistic rule in AmE (thanks to Antonio for that abbreviation) that 
an "S" placed mid-word will be voiced if the next consonent is voiced and unvoiced if the
next consonent is unvoiced.
 
"T" is an unvoiced consonent.  "M" is a voiced consonent. So the word "plastic" is pronounced 
"plas-tik" while the word "plasma"is prounounced "plaz-ma".

 
Speech really is different than spelling in many cases. Jeff, I don't know about you, but when
I try to say your "Kass-dough" out loud my tongue trips and  stumbles in the middle. 
 
Voiced "Kazz-dough" comes out smooth. So does unvoiced Casto as "Kass-toe". But switching from 
unvoiced to voiced in mid-word is awkward for most AmE speakers. Thus the "S" - "Z" phonemic rule.