In the eyes of alien colonizers, its appearance as an adult can be described as... extremely deformed.
At the same time, scientists have discovered its anomalies.
Its brain was conceived through hybridization. Though not so apparent during its childhood, functional impairments began to surface in adulthood.
After all, using a human brain to control a body more akin to a monster makes it unable to do things that most monsters can easily accomplish.
Moreover, because the nerves controlling the body are concentrated in one place, any damage to the head means direct death. Most significantly, this brain, like that of humans, is extremely delicate and fragile, intolerant of injuries.
Earth humans evolved an incomparably hardened skull to protect the brain over eons, but alien invaders have no such feature.
Although they possess similar structures, they are much softer and more flexible compared to human bones, primarily relying on muscle-like tissues for movement.
