So as long as facehugger is symbolic inbodiment of male fear of blowjob (don't remember who said that: O'Bannon, Scott, Giger or someone else)
Feels more like disgust than fear.
would it be possible it can (or at least try so) implant chestburster inside the host by another way if mouth somehow locked? To be honest. i'm talking specifically about butthole. You know because anal sex is as cruel and creepy kind of rape as oral one.
I don't think the "tube" the facehugger uses during the implantation would reach the place it needs to be for its job to work. Plus the host won't get knocked out and the facehugger doesn't fit very well down there as it does for the head. It might be easier to remove than one that tries to go to the head.
In the head, the tail chokes the neck, the fingers grabs well around the head, and the tube knocks the host out preventing any fight. Then it will kill the host if others try to remove it. While if it goes for the ass, it will have to deal with an moving angry host while being on a position that doesn't offer much advantage to it.
Call me pervert if you want