I'm wondering if DeForrest Kelly had a clause in his contract that required him to appear on screen a certain number of times. How else can you explain the fact that on several occasions, Dr. McCoy just wanders onto the bridge, looks around and then leaves. Frequently without saying a word. Its odd.
That's very true, G.C., and it is weird in light of the fact that McCoy would be the last person to blend into the background without speaking his mind!