Anakin paused his work on the part. Because Obi-Wan would very nearly kill him, all but running him through with a lightsaber. And it could also be argued being left limbless and burning alive on the bank of a lava flow was as good as killing him. And the sad truth was it would have been better for the galaxy if Obi-Wan had finished him off on Mustafar.
Anakin caught himself and started busying his hands again.
“Third, actually,” he used for his recovery. “I’m sorry, Count Dooku was his second apprentice.” He hoped Obi-Wan guess that was the source of his discomfort rather than the close mention of their duel on Mustafar. “It’s why he left the Order. He was always only meant to bridge the time between Maul and me… it would have been Knight Vergere but she disappeared at Zonama Sekot before she could be useful to Palpatine.”