In the Goblet of Fire, Harry is cut in the arm by Pettigrew. When Dumbledore learns it, he's extremely worried and wants to check Harry's arm.
When Harry told of Wormtail piercing his arm with the dagger, however, Sirius let out a vehement exclamation and Dumbledore stood up so quickly that Harry started. Dumbledore walked around the desk and told Harry to stretch out his arm. Harry showed them both the place where his robes were torn and the cut beneath them.
"He said my blood would make him stronger than if he'd used someone else's," Harry told Dumbledore. "He said the protection my - my mother left in me - he'd have it too. And he was right - he could touch me without hurting himself, he touched my face."
For a fleeting instant, Harry thought he saw a gleam of something like triumph in Dumbledore's eyes. But next second. Harry was sure he had imagined it, for when Dumbledore had returned to his seat behind the desk, he looked as old and weary as Harry had ever seen him.
"Very well," he said, sitting down again. "Voldemort has overcome that particular barrier. Harry, continue, please.
Plz explain this sentence specifically:
"Dumbledore walked around the desk and told Harry to stretch out his arm."