Converse of subject

• visit: In the early stages of the UFO controversy very few people believed that we were being visited by extraterrestrials.

Adjective modifier

• benevolent: Hence benevolent extraterrestrials are expected to avoid this abrupt course of action.

Modifies a noun

• visitation: What is it about extraterrestrial visitation that implies the availability of physical proof?

• spaceship: The belief that physical proof of extraterrestrial spaceships is kept secret is hopelessly irrational.

• spacecraft: The null hypothesis is that not one of the available UFO reports represents a genuine sighting of an extraterrestrial spacecraft.

• civilization: It has also been suggested that extraterrestrial civilizations simply haven't had enough time to find us yet.

• hypothesis: Trying to fit this case into the extraterrestrial hypothesis presents a series of problems.

• intelligence: Once extraterrestrial intelligences have been found, contact with them is less of a hurdle.

Modifying Another Word

• not: MULDER: Do we know for sure that those cells are not extraterrestrial?

Noun used with modifier

• flesh-and-blood: On the contrary, I began to realize that the ancient Egyptian gods were not flesh-and-blood extraterrestrials at all.

Preposition: in

• origin: And what's causing it may be extraterrestrial in origin.