So being the romantic idiot I am, and having a hard time defining "interest," I am wondering how to react to this.
A few days ago I went to get breakfast in the school cafeteria. I bought a cup of coffee and a fruit pie, and when I went to checkout the lady behind the cash register commented on what I was buying. I started the conversation by asking how her day was going, and since she didn't have to help ring up anyone else we kept the conversation going for about a minute. She pretty much commented on how a fruit pie would help me get through my morning cause they helped the Fantastic 4 defeat Dr. Doom in an ad in an old comic apparently (mind you I was wearing a sweatshirt with a Black Mesa logo on it). Through out the whole conversation she kept smiling and giggling at some of the things I was talking about, even though most of it wasn't funny at all. I exchanged names with her then left the cafeteria.
I have seen her work the register a few times when I go in early in the morning, most of the time there is a line, so I'll simply ask how her day was going, and most of the time she will smile at me and ask me how mine is going as well, and normally in a rather excited voice. I feel like I should at least keep talking to her, and maybe get her number, or try to ask her out at some point. This is just the first time I've noticed a girl act like this in what appears to be the most casual of conversations.