^
Ah, you've seen the wisps of smoke on the bridge too! A couple of color screencaptures from the episode seem to show that someone just off-camera might have taken a drag off a cigarette during filming and it might be one of those bloopers that many never notice, much like the shadow of the boom mike on the overhead bridge monitors above Dr. Daystrom when he speaks to the M-5 computer towards the end of "The Ultimate Computer."