[1]: 72 The plot involves a man traveling to an island where a mad scientist named Dr. Lorca is creating human / plant mutants with chlorophyll blood out of the local natives.

The captain of the ship claims that the island is cursed and tells a story of a man they picked up on a raft who bled green blood before he escaped into the sea.

Sheila is attacked in the jungle by the chlorophyll monster, but manages to escape when an unfortunate native who comes to her rescue is gruesomely mutilated by the creature.

[1]: 77  Ashley agreed, which led to his moving to the Philippines and co-producing several other films there in partnership with Romero, Beverly Miller, and Roger Corman.

[1]: 83 A prologue to the film invited theatergoers to partake in a bizarre initiation, and each patron was given a free packet of colored liquid labelled "green blood".

At a certain point, the audience was told to "recite the oath of green blood" as they tore open the little packets and drank the colored liquid inside.

[1]: 63–88 Sam Sherman came up with the idea of distributing the liquid gel-packs to the theatergoers, and said years later in an interview that he drank one of the packets, which contained an aqua-colored gel, and it made him sick to his stomach.

Nevertheless, Miller (an associate producer of the film) said he actually witnessed dozens of teenagers drinking the stuff in the theaters that he managed in Kansas City.

[1]: 74 In another gimmick, the camera zoomed in and out rapidly each time the monster killed or stalked someone, a technique that some theatergoers complained made them dizzy and was actually designed to cover up the shoddy make-up effects.

[1]: 74 [1]: 83  In 1969, a practice arose in some states (Rhode Island in particular) wherein the local newspapers began omitting the word "blood" from the titles of films they were advertising.