Did I misunderstand the "rules" for angelic possession that the show previously laid out, or did the current writers change them? Based on what happened with Castiel/Jimmy and then the whole bit about Heaven resurrecting Adam so that he could serve as Michael's vessel, I thought angels could only possess people of a specific bloodline. Yet Ezekiel was able to possess Sam's body just as easily as he possessed the body of whoever Penikett's guy was called.
I believe Castiel told Jimmy that his bloodline allowed him to comfortably host an angel presence without suffering ill effects. Lucifer's host, for instance, gradually rotted, and the other archangels had a tendency to hollow-out their hosts.