What does it mean when you kiss a girl on the cheek and she lightly laughs?

We've been hanging out/dating for over 2 months and we haven't french kissed or anything, just goodbye kisses on the lips. She says she wants this dating to be casual. We are both in our twentys and she does this almost everytime i kiss her on the cheek and sometimes when i scoot closer to her on the couch. What does her lightly laughing mean, like with her mouth closed?