be able to (do something) in (one's) sleep(redirected from are able to in their sleep)
be able to (do something) in (one's) sleep
To be able to do something with very little or no difficulty, or complete or accomplish something in a relaxed, carefree, or effortless manner. It took me a little while to get used to this job, but now I'm able to do it in my sleep! You should ask Johnny for help—he's able to do this level of math in his sleep.