Still on the thread topic:
Aliens. What are they like?,
this Twilight Zone episode entitled "Will the real Martian please stand up?" explores the 'aliens in human form' theme.
A UFO has crashed into a country pond in a blizzard and sunk out of sight, but the police discover footprints in the snow leading from the pond to a nearby diner.
Entering, they see a bus driver (4th from left), his 7 passengers and the diner owner.
Yet the driver swears he only had 6 passengers when he left the depot, so who - or what - is the 7th who's slipped in among them?