Occeus: Examine parasite.
Ah, yes. Here is the reason your test subjects roam around post-mortem: these cryptic little creatures, who embed themselves within a host body in order to take hold of their motor functions and use it as an incubator for their young. Their lifespan is rather short when left without this borrowed, protective shell.
Of course, the body eventually starts to deteriorate with time — if it hadn't already been rotting at the start. Once it has been used to its limit, the parasite will leave the old host in search of a fresher option, and the cycle begins anew.
All of these horrid, repulsive husks housing wretched creatures that only exist to self-replicate... It makes you sick. Sick with curiosity.
So little is known about them, their biology, detailed behavioral patterns, origins — it is a field ripe for study. And since you are the only scientifically-minded soul for expanses, it might as well be you who does the studying. You've already accumulated several pages' worth of notes.
They can be quite the nuisance, true, but you've nonetheless found a shared give-and-take with the strange life forms. After their extraction, the cadaver left behind is ripe for testing.