Arthur tries to move the flour like Matilda does, but when it becomes clear only a few grains will move at a time, he scoops it into a pile with his fingers.

"Alohamora!" There's a puff of flour and a smell of toast. He thinks for a moment. Then puts his hand over it and squinches his face up. The flour obediently liquefies and flows out from under his fingers.

"Oh..."