It's probably a bad thing that my first thought here was "Azusa has fat arms compared to Chihaya". Though I guess the rest of the joke is so entrenched by now that it goes without saying.

It seems that both girls have more then 2 hands. Each has two hands holding the picture and both have at least one hand showing below the picture. LOL

That's because there's somebody behind each of them, see?

Ami and Mami are such troublemakers.