hmmm; uh-huh; murmur indicating approval, comprehension, etc.
レシピをふむふむと読み進めた。
I murmured "hmm hmm" as I read through the recipe.
「ふむふむ」と上司は深く頷いた。
"Uh-huh," the boss said, nodding deeply.
先生の説明に「ふむふむ、なるほど」と彼は呟いた。
"Hmm hmm, I see," he murmured at the teacher's explanation.