This rarely happens to me because I assume I don't know people if I'm not sure I remember them. Last week, though, I walked by a girl that looked extremely familiar. Now that I think of it, she may have been the younger sibling of someone I know but I didn't realize it at the time. I just stopped and stared and I guess that made her feel uncomfortable so I just said, "Hey, how are you?" and that seemed to have broke the tension. But no, I don't know whose sibling she is.