[JustJono]

I'll speak as if there are aliens:
They probably don't care or aren't aware of us being able to see them. The anal probing crap is, well..
If you were to conduct tests by planting a probe, which hole would you use, knowing that the mouth is somewhere a probe just wouldn't fit in (the probe victim might either swallow it - or become aware of it and spit it out)? I think the only other suitable hole you'd find is the anus.

But I do believe in aliens.