Title: The scientific reasons you can 'sense' when someone is watching you
Headings: 
Because your eyes pick up on more than you know.
Because you can think your way into feeling.
Because gaze is extremely important.
Because you often wrongly assume that you're being looked at …
… but that can actually be a good thing.

Content: "Basically, eyes provide us with insights into when something meaningful is happening," she explained. This includes external-world happenings — the mammoth is charging from that direction! — as well as more personal ones: Out of all the Paleolithic dudes in the sea, you're the Paleolithic dude for me. In a species whose primary strength is communication, gaze has evolved into an extremely powerful tool for indicating interest, resources, danger, lust, and even more complex emotions like love. Because you often wrongly assume that you're being looked at …
That's not to say we always get it right. A 2013 study published in the journal Current Biology found that when we're uncertain about which way a person's gaze is directed — like when their eyes are hidden behind sunglasses — we often falsely assume that we're the target. Which, in turn, means that the feeling of being watched may become a self-fulfilling prophecy: When you think someone is staring at you from behind, you might turn around suddenly to face them, causing that person to look in your direction. It's also possible that you subconsciously noticed that person staring at you before you turned your back, and your memory alerted you to the fact several minutes later.