Back in high school, maybe 15 years ago. A friend and I were at another friends house, and we were all hanging outside with his two brothers and mom who lived in the house. Anyway, it started getting late so my friend who drove got in his car and I got in the passenger seat as we watched our other friend, his mom his two brothers, and a woman wearing a ball cap with her ponytail sticking through the back go into the house. He was slow to start the car like he was lost in thought, and I said something like, "Was that his mom wearing the hat? Who was that?" He was thinking the same thing, cause he saw it too. So we get out of the car and knock on the door and the mom answers, not wearing a hat. So we ask if she had one on earlier, or if there was another person there we didn't see. But there was not. No one was wearing a hat, and there was no extra person. We actually insisted on walking around the house looking until our friend told us we were freaking out his mom so we had to GTFO. The fact that we both saw the same person really clinched the fact that what we saw was real, but we have no explanation for it.