You've already seen them. Well, you've seen them disabled. If Peridot reactivates them they'll pick up right where they left off, planting Gems in the crust of the Earth, where they'll incubate and suck the life right out of the ground.
|—Pearl explaining Injectors to Steven, "Keeping It Together"|
Injectors are Gem machines that are used to embed nascent Gems into the crust of a planet, where they would gestate before emerging. The Injectors on Earth are currently scattered all around the Kindergartens in a state of disrepair.
The Injectors resemble bacteriophages, which are viruses that can infect and reproduce within bacteria, sometimes destroying the bacterium itself. The bottom of the machines have one large drill, surrounded by smaller ones. Thin, jointed appendages are located near the drills, presumably for walking. The upper structures sport large, red, gem-like ornaments on the top.
The body of the rig itself seems to showcase a clear panel containing within it what appears to be either an organic heart, much like the Crystal Heart located in the center of the Crystal Temple, or an artificial womb. These seemingly organic hearts/wombs are attached to the head and feet of the machine via red and blue tubes that resemble arteries and veins, respectively.
As revealed in "Keeping It Together", injectors drill into the Earth, injecting a Gem deep underground. The implanted Gem then drains the life force/energy from its surroundings in order to grow. It then forms a gemstone, and emerges from the ground, leaving behind an exit hole.
- Peridot reveals in "Too Far" that the Injectors on Earth have Era 1 drills, implying that there are more advanced versions of Injectors.
- In "On the Run", Amethyst refers to Injectors as "old Gem junk".
- Injectors can hang off walls at 90 degree angles.
- However, when Pearl threw her spear at an Injector's leg, it fell right off the cliff face.
- It is stated by Garnet that if the Kindergarten is reactivated, the Injectors will power back on and continue the project.
- Their official name was confirmed in the episode "Keeping it Together".
- However, injectors were previously mentioned during Peridot's diagnostic log in "Marble Madness".
- Peridot makes a note that the injectors on Earth are outdated.
- This implies that Homeworld has grown Gems on other planets and that they are still invading them.
- As seen in "Too Far", the interior of the drill head contains a console.
- The injectors have a very similar design and function to the virus "bacteriophage" that injects it's material into the host, which is repurposed to create more viruses.
- Additionally, their insides resemble organic hearts.
- According to Amethyst in "Guide to the Crystal Gems", the Injectors put "colorful goo stuff" in the ground and after time a Gem is formed.