be lost in thought

In “Clemency,” Chinonye Chukwu’s gripping new movie, Alfre Woodard plays a death-row prison warden so deeply absorbed in her work that she often appears to be lost in thought.

‘Who was Gil-galad?’ asked Merry; but Strider did not answer, and seemed to be lost in thought.

His gaze had wandered upward to the body revolving slowly overhead, and he seemed to be lost in thought.

He appears to be lost in thought and whatever has got his brain cells occupied is having a strange effect on his facial muscles.

For some time she seemed to be lost in thought, then she burst out passionately.