I can't ask this question without spoiling the ending of the movie, but since it was made in 1966, I figure almost everyone that wants to see it has seen it. So if you don't want to read spoilers, stop reading now.
I remember seeing Fantastic Voyage back in the 1970s, and catching it in re-runs every now and then and I've always had the same question. For those that aren't familiar with the movie, a sub and crew is miniaturized so it can be injected into a human body so they can use a laser on a blood clot to destroy it and heal an important scientist. The catch is that the miniaturization process only lasts one hour.
Close to the end of the movie, Donald Pleasence's character, Dr. Michaels, crashes the sub while everyone else is out of it, in the scientist's brain. White blood cells attack the sub and digest Dr. Michaels, who is trapped in the sub.
I can see the rationalization that Dr. Michaels was disolved or digested by white blood cells, so his molecules were spread out and wouldn't expand at the end of the hour, but the submarine is made of metal and glass and electronic components a white blood cell can't digest. While I don't see how Dr. Michaels could be digested that quickly, I can suspend my disbelief about that.
What does seem to be a serious error is that the sub is still in the scientist's brain at the end, when it would expand.
So why doesn't the sub expand at the end of the hour? Is there any explanation? I know Asimov wrote the novelization of the movie, but, while I've read the sequel, I haven't been able to find the first one.
Is there any in-universe explanation why the sub doesn't expand?