[Jack Simth]

Originally posted by Imperator Fyron:
Actually, I believe it was explained that he is programmed to become temporarily incorporeal whenever someone or something attacks him in one of the episodes. I forget if he had to control it or not though.

Actually, it went both ways, depending on the episode. The episode I suspect you are thinking of is the one where he went on the holodeck because some beings from another dimension had used it to kidnap some crew members, and only the doctor was safe from them. The incorporeal-ness you describe was a conscious only thing specific for that episode in order to deal safely with the holodeck characters in the program that was running, and applied to his entire form only. However, that was only in the one episode. In the rest, if it gets mentioned, it happens because he isn't programmed to react to the stimulus with an appropriet injury, and/or his projectors aren't up to stopping it (he held onto an object once or twice when such events were occuring - clearly his entire form wasn't becoming non-corporeal). Sometimes such antics cause problems with his holo-matrix, but not very often. The ST universe does have its contradictions.