Cool episode. Really great, but we never get to understand what the "image" really is, do we?
An alien lifeform probably.
In the Guide, Phil wonders why Belt should take the alien with him and kill it when he jumps out of the window at the end if the alien survived space before.
After rewatching this ep., I think that Belt wasn't possessed by a "normal" alien (like a ghost) who left him to bang on the shuttle and frighten michelle, but some kind of "mother" alien who detached some small aliens (like tentacles?) who frightened michelle, banged on the shuttle etc.
When belt is lying on his bed and we see the weird image before one alien is detached, it takes some time - not long, but it doesn't happen immediately.
Once the alien is detached, belt doesn't act like someone who has been freed from his possession, he acts as if he's still under alien influence.
To exert this influence on his thoughts and actions, the alien would probably have to have some physical contact with belt.
I also had the impression that when belt was on the guerny after his breakdown, that he was trying to die already to kill the alien who was connected to him - his blood pressure rose during mulders questions, maybe due to belt fighting the influence, then he collapsed, and the EMT pronounced him dead and looked very surprised when he recovered. I guess the alien took over control to prevent belt from dying.
When belt finally jumped out of the window, it was too quick for the alien inside his body to detach, and so it was killed.
I think its very amusing to watch this ep. today when we know from better pictures that the famous mars face, so important for this ep., is not the work of an alien culture, but only of erosion - like they said at the very beginning.
When Mulder and Scully are questioning some NASA scientists about the x-ray of the malfunctioning part, we hear the scientist answer before we see his face. As soon as I heard his voice, I immediatly thought of him as the bad guy in the episode. The actor is the same one who plays Maybourne on Stargate SG1. Its funny how we tend to associate actors with their characters and expect other characters they play to act the same.
For the record, the actor's name is Tom McBeath.
Susanna Thompson (Michelle Generoo) played the Borg Queen on "Star Trek: Voyager," until she was replaced by Alice Krige, the original Borg Queen, for the last episode.
In the guide Phil wonders what, if any, connection with this alien and the Greys. Personally, I thought it was fairly clear that the alien here was connected to the face on Mars; what appears to be an entirely separate race than the mythology aliens.
The reaction of the Borg Queen while driving to Houston seemed odd to me. For one thing it looked like she was driving pretty fast through a heavy downpour, with M&S trying to follow, and also who covers their face like that if they think they're about to crash?