Avada Kedavra

Causes instant, painless death to whomever the curse hits.

There was a flash of blinding green light and a rushing sound, as though a vast, invisible something was soaring through the air - instantaneously the spider rolled over onto its back, unmarked, but unmistakably dead. Several of the students stifled cries; Ron had thrown himself backward and almost toppled off his seat as the spider skidded toward him. Moody swept the dead spider off the desk onto the floor.