Human host bodies...
After looking at the series again...it seems that the aliens don't use the humans as 'marionettes' but they are actually melding with the human body, so {if one were to see the human host opened up} they would see alien and human physiology fused...
On the other hand, I'm assuming that when an alien changes bodies{from one human to another} or attacks a victim, the hand that always grabs its victim is the third hand that unmelds itself from the front...
Too, a question:
It seems they need to have their victims exposed, as I'm assuming they can't absorb through clothes, right? {In 'Epiphany' the shirt of the police officer was opened while the alien was absorbing him}.
"I need you to intervene!"-Helen Parr/Elastigirl, The Incredibles, 2004