Hapax legomenon

Hapax legomenon is a word that occurs only once within a context, either in the written record of an entire language, in the works of an author, or in a single text. The term is sometimes incorrectly used to describe a word that occurs in just one of an author's works.

From: https://en.wikipedia.org/wiki/Hapax_legomenon

Pareidolia

Pareidolia is a psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant.  Common examples include seeing images of animals or faces in clouds, the man in the moon or the Moon rabbit, and hearing hidden messages on records when played in reverse.

From: http://en.wikipedia.org/wiki/Pareidolia