When you get the Summon Spectral Assassin power, use it while doing the Dark Brotherhood quests. The Assassin will comment on each task you have to do, like "Yes, kill the Chef. Kill him and take his identity. That is true death." It's a cool little thing that I didn't notice until my second playthrough because the Assassin dies in like three hits, so I never bothered using him...


Sidequestion: Can companions die, or do they just go down on one knee for a while before getting back up with full health like story-vital NPCs do?