Rite of Passage

"It's an emotion detector." McCoy studied them both closely.

Kirk reached out to touch the smooth archway, half expecting McCoy to protest. He did not.

"See, the natives here had developed robots that looked close enough to a living person that couldn't tell the difference. Except for one thing."

"Emotion?" Spock raised an eyebrow.

"Exactly. That's mostly a glandular thing. Only someone capable of emotion can pass through those gates."

Kirk's lips twitched as he walked through. McCoy followed.

Spock remained, staring.

McCoy laughed, waving a hand. "I'm joking. It's just a doorway."

Spock remained. Eventually, turning, he walked away.