I am unable to find an explanation of the 2 distinct terms.
2
These "words" are not synonyms although they both can be used as aizuchi.
ふむふむ is onomatopoeia for the sound of agreement (similar to English Uh-huh).
そうです literally means "It is so" and can be used both for agreeing with the other party and as an analog of "I see" (invitation to continue the conversation but without a specific expression of agreement with what's being said).
answered Oct 27 '16 at 18:48
