Body double and bikini
I saw this film again last night for the first time in decades and still liked it, although the direction was clumsy and the choice of stock music in several scenes was dumbfoundingly inappropriate.
Anyway, a couple of things about the two principle actresses in the movie.
First, I can't find who played the "Visitor" as her good old mutant self. Salome Jens played both the real nurse (briefly) and then the Visitor-having-stolen-her-face-and-assumed-the-nurse's-identity. But they're obviously, originally, two different women, since they're initially seen in the same scene together and (lest you think this a use of a body double), the original, stalking Visitor has an entirely different build from Ms. Jens: lithe, angular, spry, with a longer, narrower face, in contrast to Ms. Jens's more voluptuous figure, round face, different height, build, walk, etc. Clearly they are not the same woman, and the concept of the Visitor lifting the nurse's face -- literally -- while cool, would have worked better if they'd used two actresses of about the same proportions. But back to the original issue -- who played the real, lithe Visitor? Not listed in the credits here on IMDb.
On a separate subject, there was no need for any sort of body double for Joyce Holden as Claire Erling. She was a very beautiful and quietly but intensely sexy woman (and, as another thread here says, her first kiss with Bob is a pretty steamy scene for this type of film from this period). I was also impressed by her slightly sexier than expected one-piece swimsuit in her first swimming scene, but completely knocked over by her 1958 bikini in her next lagoon scene. That was very rare in those days and while the suit is tame by today's standards it was really something back then. (I didn't remember that shot from seeing this movie as a kid: where were my priorities?) She had a great body and without knowing the competiton it's little wonder she won the "Miss Los Angeles" beauty contest in 1949 (and another one as well). I've seen Joyce in a few films -- this was her last -- and I'm glad she finaly got to show herself to good advantage on screen, even in a low-budget sci-fi like this. Good actress, too, better than this film deserved. She had been signed to Universal in the early 50s and that studio wasted her for five years before dropping her option. They really had something and were too blind to see it. A shame.