I'm curious about what's going on in this scene.
A loud, echoing crack broke the sleepy silence like a gunshot; a cat streaked out from under a parked car and flew out of sight; a shriek, a bellowed oath, and the sound of breaking china came from the Dursleys’ living room, and as though Harry had been waiting for this signal, he jumped to his feet, at the same time pulling from the waistband of his jeans a thin wooden wand as if he were unsheathing a sword. But before he could draw himself up to full height, the top of his head collided with the Dursleys’ open window, and the resultant crash made Aunt Petunia scream even louder.
Harry felt as if his head had been split in two; eyes streaming, he swayed, trying to focus on the street and spot the source of the noise, but he had barely staggered upright again when two large purple hands reached through the open window and closed tightly around his throat.
“Put - it - away!” Uncle Vernon snarled into Harry’s ear. “Now! Before - anyone - sees!”
“Get - off - me!” Harry gasped; for a few seconds they struggled, Harry pulling at his uncle’s sausage-like fingers with his left hand, his right maintaining a firm grip on his raised wand. Then, as the pain in the top of Harry’s head gave a particularly nasty throb, Uncle Vernon yelped and released Harry as though he had received an electric shock - some invisible force seemed to have surged through his nephew, making him impossible to hold.
(Order of the Phoenix, Chapter 1, Dudley Demented).
The other elements of this incident are explained later in the book. The crack is Mundungus Fletcher Disapparating. The cat belongs to Mrs Figg and is keeping watch on Harry/Mundungus. The shriek and the broken china come from the Dursleys themselves.
Yet the force that makes Uncle Vernon suddenly let go of Harry is more difficult to fathom. It's possible that it was a normal electrical shock as a result of static. However, it seems far more likely that there was something magical going on. Vernon had a hold of Harry for several seconds before releasing him so it clearly wasn't that he couldn't touch Harry at all (as was the case with Quirrell). I'm not clear on whether or not the magic was connected to the pain in Harry's head.
What exactly caused Uncle Vernon to suddenly let go of Harry?