Could be that in order to lure 'em in, it's got some method of making them mentally unstable first. Like a breach of defense.

[ Anyone in their right mind probably wouldn't feel up to responding to some kind of call, otherwise. Though... ]

It's too early to say either way. For now, it seems like we've at least got some level of defense against it... or maybe it just hasn't tried again since our arrival. But yeah, I'm not too confident in their survival out here, especially if they were coming out unprepared.