I'm looking for the name of a movie from the 1950s. It involved an alien race that put a forcefield around a major city (Maybe LA) and some survivors were stuck inside. The most identifying thing I can remember is that the aliens used spears and one of the heroes discovered that if he knocked the tip off and stabbed one of the aliens with the hollow shaft its own body pressure forced its blood out through the spear and killed it.
The movie is The Slime People (1963). The hollow-shaft impalement scene is at the end of the trailer.
From the Wikipedia entry:
The image that sticks with me is that of the contorted dead man, still standing, that the heroes find embedded in the solidified fog.
It could be Invasion 1965