“When I looked up from my reverie, I realized that a figure with a large white beard wearing a brown robe over his clothes had appeared utterly silently quite nearby on my left. I was so startled that I felt like I was outside myself watching the scene. My eyes widened, I jumped involuntarily, my heart pounded. I thought, wildly, “Oh no, what if I have accidentally come to the home of the wrong hermit?”. But as soon as I looked at his face, I recognized it from photos I had seen. Oddly enough, it was not the more recent photos where I saw the resemblance, but to a much older black and white photo of him when he was young. “It’s you!” I managed, idiotically. Grothendieck stood impassively. In one hand, he held a short pitchfork loosely at his side. It reminded me of his doodle of devils with pitchforks around the Grothendieck–Riemann–Roch formula. His free hand rose, brandishing an admonitory finger. “Il ne faut pas entrer,” he said, advancing slowly toward me. I tried to form some sentences about visiting, but Grothendieck did not react. He continued to walk slowly toward me, wagging his finger, telling me that I shouldn’t be in here disturbing him, and asking me how I got in here.”
Hat-tip to this blog post in the Scientific American for pointing this out.