By the way she made eye contact with strangers for a solid second before abruptly breaking off, I could tell that she was friendly, but socially awkward. Mid-forties, by my estimation - skinny, pale, with dark brown hair. I was standing in the subway car, and she was sitting near me, marking up a printed document.
While placing the papers into her bag, she accidentally touched the man next to her with her elbow. In response to his instinctual glance, she said, "I was just doing my homework," and giggled slightly. The man offered a polite, but evasive laugh, and looked away soon after.
I couldn't help but chuckle, and following me shortly, others began to join in. An old man's roaring laughter caused the laughter of all others to escalate, until the subway car was filled with the noise. He could barely breathe as he said, "Doing homework... that's hilarious!"
Looking at the woman, I said, "You didn't make that up," but I didn't make enough of an effort to speak over the crowd.
Still giggling, she asked, "What?"
Before she could inhale, my hand was clamped onto her throat. Speaking into her ear, I repeated, "You didn't make that up, did you?"
Shocked and afraid, she replied, "Yes, it was just..."
My thumb, which was lodged under her jaw, pressed farther up under the bone.
She yelped and said, "... I... I must have seen it in a movie or something."
I was back in my standing position, and the woman was still direly confused, when the laughter began to die out. I think I noticed before she did that she'd pissed herself during our little conversation. I pointed a finger and began chuckling, and within seconds, the whole car was again filled with laughter.