Bull turned his head to avoid looking right at the flash, but he did catch sight of the harpies. They were horrifying, and Bull suddenly had no qualms with killing them.

He grunted when Geralt used him to get out of the way; in a single, surprisingly quick movement, Bull swung the sword to catch the harpy's neck as soon as it was within reach, trying to avoid those talons and failing wings.

Maybe there was a trick to killing them, but he figured hacking off a head was a solid start.