To both Harry and Mr Weasley’s shock, the sword shrunk down in size so that, while still obnoxiously large, it wasn’t as ridiculously massive when Harry was holding it. Though it was still heavy as well, Harry felt like the blade was adjusting itself to accommodate for Harry’s own size and strength. If that were the case, then when he took the potions, he somehow knew the goblins were in possession of required to fill him with enough nutrients to make up for his childhood when he had free time, the sword would adjust itself then.