‘We know you're up to something funny,’ said Aunt Petunia.
‘We're not stupid, you know,’ said Uncle Vernon.
‘Well, that's news to me,’ said Harry, his temper rising, and before the Dursleys could call him back, he had wheeled about, crossed the front lawn, stepped over the low garden wall and was striding off up the street.
He was in trouble now and he knew it. He would have to face his aunt and uncle later and pay the price for his rudeness, but he did not care very much just at the moment; he had much more pressing matters on his mind.
Harry was sure the cracking noise had been made by someone Apparating or Disapparating. It was exactly the sound Dobby the house-elf made when he vanished into thin air. Was it possible that Dobby was here in Privet Drive? Could Dobby be following him right at this very moment? As this thought occurred he wheeled around and stared back down Privet Drive, but it appeared to be completely deserted and Harry was sure that Dobby did not know how to become invisible.