口ごもる

その来たばかりの子はおどおどして口ごもった。

The new boy had a nervous stammer.

あいつは口ばかりで、誠意がないね。巧言令色少なし仁とはよくいったもんだ。

They say fine words are no virtue if they're insincere and that's him in a nutshell. He's all talk but doesn't mean a word of it.

彼はまるで何でも知っているかのような口ぶりだ。

He talks as if he knew everything.