Translation of "Mumbled" in Japanese

"Hrmm," mumbled Professor Takeda as he twisted his moustache.

「ふむ」 武田先生は口ひげを捻りながらうなった。

- The shy boy murmured his name.
- The shy boy mumbled his name.

その内気な少年はぼそぼそと自分の名前をつぶやいた。