If the hiphugger sees the other facehuggers getting smashed, it will leave and spread an alarm scent.
She is then full of chemicals that are making her horny, so the next critter has a much easier time impregnating her. If there is only one, the facehugger fills her up, and leaves. If there are more 'huggers, they are working her mouth over too, giving her fluid to keep her horny, lactating, and dominated. The main one is a hip hugger that comes in and impregnates her.
They work in groups, the majority are facehuggers to block her vision and keep her aroused (plus pumping fluid that she is forced to drink). One being a facehugger, one being a hiphugger.
