You may recall the image of David Tennant, Doctor number 10, smoking many cigarettes simultaneously.

Frequently, it is a GIF, with a caption of “I can’t do it!”

It turns out that it was a part of a video, a musical number, done with Catherine Tate (Donna Nobel) and John Barrowman (Captain Jack Harkness) as an appreciation to Russell T. Davies and Julie Gardner when they left the series,

And here is the video: