How to recognize an Invader

THE HARD FINGER



Some of them have a kind of deformity in their little finger, which is straightened out and cannot be bent.


NO HEARTBEAT

		They have no pulse and no heartbeat but can induce the semblance of both with the use of specially concealed devices for short periods of time.



An alien was infiltrated in the American spatial program, personifying the astronaut Hardy Smith. Everytime the doctors had to examine him, heart beat, blood pressure, etc., he used such devices to cheat the Human doctors, that was seen in the episode “Moonshot”.


THE REGENERATION

		They need to regenerate themselves at regular intervals of time, or they will die.


BURNING UP



When they die, they glow red and incinerate, usually leaving little or no trace. Sometimes just a very little vestige of cellulose ash is left, as stated in the episode "The Peacemaker".


NO BLOOD



When they are wounded, they don't bleed or bruise.


ANATOMY

		Their internal anatomy, muscular system and bone structure, is completely alien to terrestrial life forms and only outwardly mimics Humans out of necessity.


NO EXTERNAL PAIN

		The Invaders are not susceptible to external pain, when they are wounded they usually don't feel any pain. The same does not apply to internal organs, since an Invader named Blake showed some visible signs of terrible pain in the episode "The Enemy".


NO problems with the sunlight in their eyes

		The Invaders eyes are not susceptible to direct exposure to the sunlight. The Invaders can look direct to the sun with no problem; they don’t even blink when they look at the sun. Obviously their home planet has a brighter sun, so their eyes can tolerate higher levels of light, than any human being.



We could clearly see this in the episode "Doomsday Minus One", when David was having difficulties to keep his eyes opened in a car, which was being driven in the desert, with the sun just ahead. So, never expect to see Invaders wearing sun glasses, they do not need them.


EMOTIONS

		They usually don't show any emotions. It's evident that they control them very well, most of them are cold and emotionless, but some of them proved to have some strong emotions and even fear of their own death.

Many, once in their Human form for a period of time, playing their Human roles in their Human communities, have either learned or adopted positive Human attributes such as compassion, sacrifice, even love. Some examples of aliens with strong emotions are Vikki, Anne Gibbs, Blake, Nick Baxter, Claire, Keith, etc...
Whether this is learned behavior, individual Invaders “going native”, or simply the Invader intense indoctrination wearing off over time is a topic of debate of Invader behavioral researchers around the world.