Dean snorts, but doesn't reply to Cassie, as they're now right next to Kaylee. Also, he would be laughing if he knew what Cassie thought about Kaylee. Innocent is definitely not something Dean would use to describe Kaylee.

But then again, Dean isn't exactly innocent when it comes to Kaylee, so. Maybe it's a matter of perspective.

"You havin' fun, Kaylee?" Dean asks, attempting to get a conversation started. He's determined to get Cassie to be more than just polite.