"But, sweeper," Harry said. "The wizards could not help me to devise a method through which I would surely win against Voldemort. However, people say that you could lend me a hand. Could you?"
Lu-Tze nodded and continued to tend to his bonsai mountain. "Rule One is: Do not act incautiously when confronting a little bald wrinkly smiling man," he said.
"Erm, ok, but do you know how I can win against Voldemort?"
"As they say: If you understood the solution, you would know it by now."
"I have nothing more to say. There's floor left to be swept."
Harry stared at the little bald wrinkly smiling man, wondered what his chances to pit Lu-Tze against Voldemort were, decided that there were none, then looked at the man again, stared hard, walked towards him and touched him on the shoulder.
"Yes?" Lu-Tze asked.
"May I have your nail clippings?"
Lu-Tze measured him from feet to eyes, then took out a little bag out of his pocket. Harry started. Sure, he'd asked, but he hadn't really expected to be taken seriously and he certainly hadn't expected the man to have any on him. He opened the bag curiously and saw that, surely enough, he had nail clippings now. He bowed low. Lu-Tze nodded, then went back to his floor.
Harry left holding the little bag close to himself. Polyjuice, here he came!