It's mainly the crush of the one on the left (their right), hence why she's too nervous to make proper eye contact, let alone open her mouth. 



So after that lighting test that I made earlier, I was interested to see if I could use the things I had learned there in order to make something other than a bright sunny environment with an intense backlight. I tried to make something that looked more indoors-y, but that ended up looking sort of awful, so I scrapped it and made this instead, which I think it looks way more neat. 

I also tried to make a sort of seat belt effect thing with the strap on their purse. That strap may or may not have ended up being a little too loose considering to how tight the cleavage fitting is. Also, speaking of that strap, thank you to WanderTones for the idea of adding a clasp to it so they can take it off without undoing their braid.