What if : An Alien showed up at your door. (What if ? Vol.2)

You are woken up by a knock at your door. It's currently 3AM (perhaps you weren't even sleeping yet). The knock is light, as if whoever-- or whatever is knocking-- was hollow. 

Let's cut to the chase. You open the door and see : ... what do you see ? How do you imagine aliens ? Are they green guys with big heads, shapeless blobs, or something else ? 

Write it in the comments ! What does it look like ? And what do would you react ?