Well yeah. Captain Keyes was kept alive by the Flood who were intent on harvesting his memories and knowledge. But he was a strong old coot and fed them as many trash memories as he could, like meeting the mother of Miranda and his transformation into a footsoldier for the Flood. I just think it's really, really creepy that even after you're infected some amount of your consciousness remains so that you can actively notice how your body has changed.
That's why the Flood are so interesting compared to the Covenant. They're a parasite at heart and there's a lot of biology at play. Like all the soldiers who were possibly immune to the transformation, like Sergeant Johnson, a relic of the Spartan-I program. That genetic modification made them immune to the Flood.