Hi Mr. Spotnitz,
First and foremost, thank you for this opportunity. I watched The X-Files as a teenager. And have since rewatched it several times over the years. It is my go to comfort show.
Thank you for the question! There were certainly times when the medical jargon -- and a lot of the technical dialogue both characters had -- was challenging and required several takes to get right, but my overwhelming memory is of how incredibly well prepared David and Gillian were. As you know, this was in the era of doing 24 episodes of television per season, and working from early morning Monday to early morning Saturday every week, often in inclement weather. With either Mulder or Scully or both characters featured in the vast majority of scenes we shot. Just the physical challenge of it was astounding. And yet David and Gillian invariably came in prepared and not only knew their lines -- even the difficult ones -- cold, but delivered them with grace and power. As writers and producers watching dailies every day, our admiration for their work ethic was boundless.
David's nodding at Gillian (and visa versa) was not something we scripted, but a performance choice. And of course the chemistry the two of them brought to every scene they did together was nothing short of magic. :)