McCoy: A negative attitude is no good to us. We can’t just leave them out there, wherever they are.
Spock: We shall continue sensor scans, Doctor. At the moment, that is all we can do, except hope for a rational explanation.
McCoy: Hope? I always thought that was a human failing, Mister Spock.
Spock: True, Doctor. Constant exposure does result in a certain degree of contamination.
Star Trek — Season 2: Episode 17 — “The Gamesters of Triskelion”