Exos were made using radiolarian fluid(vex milk) to fight the Vex. The Vex all share a single hive mind. Asher Mir was most likely turned into a Vex. One blue-eyed harpy was severed from the rest of the Vex mind and imitated the personality of Failsafe’s late captain Jacobson. There have been two other sightings of a so-called “friendly harpy.” One was during the Vex offensive on Earth where it beeped out “ASSISTANT” in Morse code. This harpy could be controlled by Asher if he survived being converted. The other sighting was on Europa. If you kill a certain wyvern near Mithrax’s downed skiff in Asterion Abyss, you will be told to go to Nexus where a “friendly harpy” will give you a test of light or darkness. Radiolarian fluid converts all it touches to Vex. [u]BONUS:[/u] Clovis Bray attempted to create a line of exos infused with Vex minds and built to control the Vex. The first attempt failed and the project was discontinued. My turn to ask questions to the rest of you! Why does Radiolarian fluid hurt exos? It’s literally their blood!

Funky milk makes anything that touches it vex, said milk also wants to make everything in the universe vex. (They can also manipulate time to a degree that I don’t know much about, I think bungie has even less of an idea.)