Seen something others can't see
How many times have you felt like someone was watching you or have seen something in the corner of your vision flash past? You may have looked at a window in a house to see a person but when you look back a second later or take a double take there is nothing there.
Many people pass it off as a trick of the light or with a scientific reason as to what is could have been, but if it happens to you you know what you saw even if you cant explain it. Learning to develop this aspect of your already active abilities will start you on a journey of understanding.