I've been rewatching the first Alien movie (again) and started thinking about the egg/facehugger which Kane disturbed.
The facehugger needs an orifice of a host to be able to impregnate it. It doesn't have any way of "piercing" or burrowing its way into a host, other than via an orifice. So...
How did it instinctively know to leap towards Kane's face?
It could have been a lot more "trial and error" flailing around the general vicinity, hoping to find *any* orifice. But it didn't. It went straight for Kane's helmet/face.
(It should be noted that in our universe (and in the universe of Alien) there is no gusrantee that other life forms - if encountered - will have a mouth, lips, teeth, tongue, ears, or even a face. So the facehuggers are harming their own survival by limiting themselves to evolve with a proboscus which targets ONLY THOSE living hosts in the cosmos, that happen to have a face, mouth, esrs etc...)