I think that when you choose the part to quote for the trailer, you should make sure to leave the viewer wanting more. The viewer should be thinking "what's next?" and then go looking for it.
"Bag of element 79," Harry said, and withdrew his hand, empty, from the mokeskin pouch.
Most people would have at least waited to get their wands first.
"Bag of okane," said Harry. The heavy bag of gold popped up into his hand.
Harry withdrew the bag, then plunged it again into the mokeskin pouch. He took out his hand, put it back in, and said, "Bag of tokens of economic exchange." That time his hand came out empty.
Harry Potter had gotten his hands on at least one magical item. Why wait?
"Professor McGonagall," Harry said to the bemused witch strolling beside him, "can you give me two words, one word for gold, and one word for something else that isn't money, in a language that I wouldn't know? But don't tell me which is which."
"Ahava and zahav," said McGonagall. "That's Hebrew, and the other word means love."
"Thank you, Professor. Bag of ahava." Empty.
"Bag of zahav." And it popped up into his hand.
"Zahav is gold?" Harry questioned, and McGonagall nodded.
Harry thought over his collected experimental data. It was only the most crude and preliminary sort of effort, but it was enough to support at least one conclusion:
"Aaaaaaarrrgh this doesn't make any sense!"
The witch beside him lifted a lofty eyebrow. "Problems, Mr. Potter?"
"I just falsified every single hypothesis I had! How can it know that 'bag of 115 Galleons' is okay but not 'bag of 90 plus 25 Galleons'? It can count but it can't add? It can understand nouns, but not noun phrases that mean the same thing? The person who made this probably didn't speak Japanese and I don't speak any Hebrew, so it's not using their knowledge, and it's not using my knowledge -" Harry waved a hand helplessly. "The rules seem sorta consistent but they don't mean anything! I'm not even going to ask how a pouch ends up with voice recognition and natural language understanding when the best Artificial Intelligence programmers can't get the fastest supercomputers to do it after thirty-five years of hard work," Harry gasped for breath, "but what is going on?"
"Magic," said Professor McGonagall. She shrugged.
"That's just a word! Even after you tell me that, I can't make any new predictions! It's exactly like saying 'phlogiston' or 'elan vital' or 'emergence' or 'complexity'!"
Professor McGonagall laughed aloud. "But it is magic, Mr. Potter."
Harry slumped over a little. "With respect, Professor McGonagall, I'm not quite sure you understand what I'm trying to do here."