"Okay—I'm just speculating," Dean closed his eyes.
Fred asked the question like a learned professor, speculating on a universal problem of time, space and the creation of the universe.
I'll write it in general terms, speculating on how difficult it is to maintain both lives, operating one incognito.
Dean spent much of the trip speculating on the reason for the law man's visit.
I moved to the want ads, speculating on what I'd be doing with my time in the future but nothing caught my eye.