V shaped eyebrows and a small tear too. I think she's trying to maintain her STRONGEST attitude, but with Yuuka being so upclose and personal with Cirno's face, she's probably a getting a little dazed and embarrassed. The look Yuuka is giving Cirno is beautiful and intimidating at the same time, so that most likely doesn't help.
You know, that would actually be quite a decent doujin plot.
(laughing) Oh, my, YES! Dovetails right in to one I have locked up in my pointed little head. Never see the light of day (WAAAAY too MarySue for its own good), but I'll leak this much: it revolves around "An der schönen blauen Donau".