For millennia, the pods floated in space like spores, propelled by the solar winds, some occasionally landing on inhabited planets.

Upon landing, they replace the dominant species by spawning emotionless replicas; the original bodies disintegrate into dust after the duplication process.

Physician Miles Bennell, played by Kevin McCarthy, gets away from the town and tells his story to another doctor.

The final shot is Bennell standing on a highway shouting warnings at passing cars and into the camera.

After landing on Earth, they assimilate leaves and become pink flowers; the aliens eventually grow the larger 6-foot-long (1.8 m) pods.

This time, those subverted can scream in an eerie high-pitched alien voice, which is apparently used to alert other pod people of humans in their midst.

As one character stabs his almost-formed pod replacement, a replica immediately emits the alien scream.

In the closing scene, Veronica Cartwright's character is happy to see the hero, played by Donald Sutherland, only to hear him emit the alien scream.

Their extraterrestrial origin is hinted (suggested through a pan-in of the galaxy during the opening credits, and a statement by the replica general they traveled "light-years").

As their invasion snowballs, the pod people transform humans by injecting them with the substance under the guise of "influenza vaccines".

Carol takes a photograph of a human after conversion, but the conflicting memories give the replica a heart attack.

[2] The manner in which the pod people outwardly resemble the people they have replaced, but are completely empty and soulless, reflected the viewpoint that the Communist regimes have destroyed the "real" nations that previously existed before they came to power and replaced the "authentic" national identities and cultures with something artificial and profoundly distasteful.

[2] Likewise, the particular place where the pods have landed in is a small town in rural California, meaning that Americans are the ones being targeted for replacement by the pod people, which served as a metaphor for how many Americans felt threatened by Communism, whose triumph was widely feared to be marking the end of the "real" America.

The vegetarian metaphor literizes Red Scare rhetoric of the "growth" of Communism as well as the idea that revolutions are made by planting seeds.

There is a scene where the pod people are assembled in the town square, where a loud speaker reads out the day's orders; it is the quintessential fifties image of socialism.

[4] Lim wrote that the pod people "...with their dead-eyed stares and moblike behavior, they could also be seen as embodying the most sinister tendencies of the Eisenhower-McCarthy era.