Finger job

When a girl strokes your cock with just one finger, eventually bringing you to orgasm. After I was completely naked, she sat me down, handcuffed my wrists behind the chair, and used nylon rope to tie my ankles to each chair leg. She stood up and looked down at me, smiling and looking amazing in her sports bra and short shorts. She held her index finger in front of me. “One finger. That’s all I need to make you cum.” She read the puzzled expression on my face. “Oh, you don’t believe me? Why don’t we make a wager. If I make you cum within 5 minutes, I’ll leave you here for the next hour.” My heart stopped for a split second. “If I don’t…” she leaned in to whisper in my ear “I’ll let you handcuff me instead.” My jaw dropped at the idea of being able to turn the tables on her. “I’ll take that as a yes, then?” she said, smirking. I nodded, although my throbbing ejection may have been clouding my judgment. “All right,” she pointed to the clock. “Your 5 minutes start now.” She leaned over, her face just in front of mine. With just her index finger, she started slowly and lightly stroking my cock from my shaft to the tip. It felt great, and it made my wrists and ankles twitch against my binds, but I didn’t see how she was going to make me cum from it. She then gave me 5 quick, hard finger strokes from the bottom to the top of the underside of my erection. She suddenly stopped stroking me, stepped back, folded her arms and beamed. “You lose!”