Example : As distant and bemused as a professor listening to the prattling of his freshman class.
Lost in thought.
A preoccupied frown.

Synonyms : bemused, lost

Example : Became more and more haunted by the stupid riddle.
Was absolutely obsessed with the girl.
Got no help from his wife who was preoccupied with the children.
He was taken up in worry for the old woman.

Synonyms : haunted, obsessed, taken up