"Do you want to move a little closer?"

"I thought you'd never ask."

The two sweethearts didn't notice Malfoy's approach, nor the snowball
that stopped at the top of its arc, a couple of yards from them.

They also didn't notice his flight through the air, or his hasty
retreat from the legendary poltergeists.

And they certainly didn't notice their invisible guardian leaving the
clearing as silently as he had arrived.

If they noticed that Harry was in a foul mood that evening, then they
assumed it was just because he had been left alone in the Castle all day.