In BioShock Infinite, as I walk around I'll hear Elizabeth or Booker say "huh", "hmmm", etc. Does this mean anything? It doesn't seem to happen when I do anything specific like standing around for too long, they just do it.
There is no meaning behind these 'grunts'. As you look around, the 2 characters are meant to have passing sounds as to feel more alive and realistic.
There are no puzzles or secrets to be found just because some of the characters make a sound.