Huh?

“New research by Mark Dingemanse and colleagues at the Max Planck Institute for Psycholinguistics … has uncovered a surprisingly important role for an interjection long dismissed as one of language’s second-class citizens: the humble huh?, a sort of voiced question mark slipped in when you don’t understand something. In fact, they’ve found, huh? is a “universal word,” the first studied by modern linguists.