Page 5 is completely missing the point LMAO.
Ranka's not saying, "hmm hmm"; they're all going "あんあん" (moaning sounds), and Kikuri is fucking around by saying she loves red bean filling (which is pronounced ann, the same as the moaning sounds).
That's why Ranka goes "Why are you making us moan all of a sudden" on the next page.
EDIT: Page 19 incorrectly puts Chinana's name as Takenana (likely due to the kanji in her name 竹奈々, with 竹 being read as take, but her name is confirmed to be read as Chinana)