[Snape has approached Harry, Ron and Hermione]

Now, what would three young Gryffindors such as yourselves be doing inside on a day like this?

We... [Snape looks to her, expecting an answer]...we were just...

You ought to be more careful. People may think you're...[Snape notices Harry eyeing him cautiously. He glares sharply at Harry]...up to something.