Although the words “mentioned” and “declared” have similar meanings, they are different because
one is figurative
one is a euphemism
they have distinct denotations
they have distinct connotations

Although the words “mentioned” and “declared” have similar meanings, they are different because they have distinct denotations. Denotations give the literal meaning of the word. According to macmillan dictionary, “mentioned”  refer to something briefly without going into detail and “declared” means saying something in an empathic manner. 

the words "strangest" and "unusual" suggest (:

martians or other types of aliens represent a unique fear as opposed to zombies. vampires and other types of monsters.   in most sci-fi stories, aliens come from other worlds and have different or more advanced technology.   abductions and experimentation on human bodies that involve these technologies, or the use of these technologies against human beings and the use of unknown "powers", are a type of fear that's different from that of other types of monsters.