And then many things happened at the same moment.
They heard an uproar from the distant boundary of the school as what sounded like hundreds of people came swarming over the out-of-sight walls and pelted toward the castle, uttering loud war cries. At the same time, Grawp came lumbering around the side of the castle and yelled, “HAGGER!” His cry was answered by roars from Voldemort’s giants: They ran at Grawp like bull elephants, making the earth quake. Then came hooves and the twangs of bows, and arrows were suddenly falling amongst the Death Eaters, who broke ranks, shouting their surprise. harry pulled the Invisibility Cloak from inside his robes, swung it over himself, and sprang to his feet, as Neville moved too.
In one swift, fluid motion, Neville broke free of the Body-Bind Curse upon him; the flaming hat fell off him and he drew from its depths something silver, with a glittering, rubied handle —
The slash of the silver blade could not be heard over the roar of the oncoming crowd or the sounds of the clashing giants or of the stampeding centaurs, and yet it seemed to draw every eye. With a single stroke Neville sliced off the great snake’s head, which spun high into the air, gleaming in the light flooding from the entrance hall, and Voldemort’s mouth was open in a scream of fury that nobody could hear, and the snake’s body thudded to the ground at his feet —
Harry Potter and the Deathly Hallows – J.K. Rowling