So, here’s the song that Yotsuba’s singing on page 14:
Can’t find the specific model of phone Miura is referring to, but au is a real phone manufacturer in Japan. Kind of interesting that the model number is “zed eks” rather than the Americanian “zee”.
Chiyo-chan’s dad putting in another cameo there.
Yotsuba’s kaomoji is definitely the best part of the chapter.