「あー、なるほど！」　Wow! I see 「知らなかった！」 I didn't know that 「めっちゃおもしろいね」　That's very interesting (casual) 「とてもおもしろいですね」 (formal) 「おしえてくれてありがとー」 Thank you for explaining (teaching) to me (casual) 「えー、さんきゅー！」(casual) other expressions ほうほう *pronounce like ho-ho- (deeply interested) ふむふむ(otaku) なるほど is good word to express your interest. I often say it, too. If you have any question, I always help you :)

I usually using this word "Wow, I see!" = ええ、なるほど "I didn't know that" = 分かりません "That's very interesting" = それは面白い

I'm Japanese. maybe I think you meen "Aizuti" for example like "uh-huh" "yeah" "Aizuti" of japanese is "うん、うん" "ふ〜ん" "へ〜" "ええ" "はい" almost everytime. You can say "うん、うん" when you want to say "I see" "I think so too" "right" And "ふ〜ん" "へ〜" meens like "I see" "that's very interesting" ええ is formal of うん、うん はい is yes.