The eyes get widened and assume a peculiar starring look which is sure sign of the
over-activity of the pancreas.
Answers
Answer:
A complex biological system must work in concert for gaze detection to occur.

PHILIP PERRY
A full-time writer and blogger for the past 5 years, Philip's work has appeared on Your Tango, Pop Sugar, STEMJobs, Hack Writers, NJ.com, inTravel Magazine, and more. He has lived in Africa, Asia, and for a short time in Europe, and can be found in New Jersey with his friendly cat Selena.
20 August, 2017
Say you're engrossed in a task, scrolling through your phone or reading a book. Suddenly that creepy, prickly feeling grabs hold of you. Someone's staring. You turn to find out who it is. Be they friend or foe, the feeling itself seems like an eerie sort of 6th sense. It's also a necessary part of being human, an adaptation that kept our ancestors alive. So how is it that we can even do this? It's actually an important feature of our sight, our brain, and certain social aspects of our species.
The biological phenomenon is known as "gaze detection" or “gaze perception." Neurological studies have found that the brain cells that initiate this response are very precise. If someone turns their gaze off of you by turning just a few degrees to their left or right, that eerie feeling quickly fades. Scientists suggest that a complex neural network is behind gaze detection.
So far, the neural network responsible in humans remain unidentified. A study with macaque monkeys however, discovered the neurological circuits responsible for their gaze detection, even getting down to the specific cells involved.
We do know that ten distinct brain regions are involved with human sight, and there may be more. The visual cortex is the main contributor. This is a large area at the back of the brain, which supports many important aspects of sight. But other areas, such as the amygdala, which registers threats, must also be involved with gaze detection somehow.
Humans are sensitive to the gaze of others. When another person changes the direction of their attention, we automatically follow their gaze. It's more than just being predators, who as a group are naturally sensitive and drawn toward changes in the environment. It also has to do with the cooperative and social nature of humans and how we've depended on one another throughout our history and development.

The visual cortex. By Coxer, Wikimedia Commons.
Another reason, if you look at human eyes in contrast to other animals, the sclera or white part surrounding the pupil is far larger. In most other species, the pupil takes up most of the eye. This is to obscure their eyes from predators. But for humans, a larger sclera allows us to notice the direction of each other's gaze quickly.
Of course, we don't have to be looking directly at someone to tell whether or not they're staring at us. We can also evaluate the direction of their attention through our peripheral vision. But this method is much less accurate. A pair of studies finds that we can only accurately detect whether or not someone is staring at us within four degrees of our “central fixation point."