Both Nicholas Lea and Laurie Holden had to learn Russian for the episode, which, according to the former "was 'not had'." Holden and Lea worked diligently together to perfect their pronunciation, with Holden explaining, "We'd come up with these fun ways to test ourselves to know if we had really nailed it. Show tunes come to mind, but I also remember this one time my dialect coach had me call a Russian friend of his on his cell phone to see if he could understand me. I passed the test." "Patient X" was the first episode in which Lea was credited under the "Also Starring" tag, alongside Mitch Pileggi and William B. Davis.