Ever looked at a face on a billboard and creepily felt their gaze following you as you moved past?
It's called the Mona Lisa Effect, and now scientists have explained how it happens – or how it doesn't, at least with Leonardo Da Vinci's iconic painting.
"People can feel like they're being looked at from both photographs and paintings - if the person portrayed looks straight ahead out of the image, that is, at a gaze angle of zero degrees," says Professor Gernot Horstmann, of Germany's Bielefeld University, and the co-author of a new study.
"With a slightly sideward glance, you may still feel as if you were being looked at."
To test the observation, Horstmann and colleague Dr Sebastian Loth had 24 people look at the Mona Lisa on a computer screen and assess the direction of her gaze.
The participants sat in front of the monitor and a simple folding ruler was positioned between them and the screen at several distances.
The participants indicated where Mona Lisa's gaze met the ruler.
To test whether individual features of Mona Lisa's face influenced the viewers' perception of her gaze, the researchers used 15 different sections from the portrait - starting from her entire head to only her eyes and nose.
Each image was shown three times in random order and halfway through the session, the researchers also changed the distance of the ruler from the monitor.
Of more than 2000 assessments, nearly every single measurement indicated that the Mona Lisa's gaze was not straight on but to the viewer's right-hand side.
"The participants in our study had the impression that Mona Lisa's gaze was aimed to their right-hand side," Horstmann said.
"More specifically, the gaze angle was 15.4 degrees on average. Thus, it is clear that the term Mona Lisa Effect is nothing but a misnomer.
"It illustrates the strong desire to be looked at and to be someone else's centre of attention - to be relevant to someone, even if you don't know the person at all."
Do you suffer from text neck?
It turns out your smartphone is quite literally a pain in the neck.
Researchers say the large majority of the world's 3.4 billion smartphone users are putting their necks at risk every time they send a text.
"Text neck", as it is colloquially called, places stress on the spine and alters the neck's natural curve, increasing the likelihood of associated soft tissue discomfort.
A recent international study highlights the high ergonomic risks to smartphone users, particularly young people, who are experiencing neck pain earlier than previous generations.
Researchers from Khon Kaen University video recorded 30 smartphone users in Thailand aged between 18 and 25 years, who spend up to eight hours a day on their phones.
Using a Rapid Upper Limb Assessment tool (RULA) to measure ergonomic risk levels, they found that the average score for the participants was six, compared to an acceptable score of between one and two.
RULA has been used to assess the ergonomic impacts of desktop computers and laptops in the past but this is believed to be the first time the tool has been used to assess ergonomic risk levels of excessive smartphone use.
Dr Rose Boucaut, a University of South Australia physiotherapist involved in the paper, says the awkward postures adopted by smartphone users can adversely affect the soft tissues.
"Smartphone users typically bend their neck slightly forward when reading and writing text messages," she says.
"They also sometimes bend or twist their neck sideways and put their upper body and legs in awkward positions.
"These postures put uneven pressure on the soft tissues around the spine, that can lead to discomfort."
Some smartphone companies are now sending unsolicited messages to their customers notifying them of their average time spent on daily smartphone use.
Robot hate on the rise?
It's not quite The Jetsons, but we're seeing more and more robots in everyday life.
Now researchers from Germany's University of Wurzburg are reporting growing skepticism about them, and especially their roles in the workplace.
An analysis of data from more than 80,000 European residents found that, while people positively saw robots as useful helpers for mundane or dangerous tasks, they weren't keen on robots acting as drivers, surgeons or caretakers.
Some other interesting patterns emerged: women were more skeptical than men about robots, as were blue collared workers when compared with people in office jobs.
And, contrary to assumptions that the elderly are a bunch of technophobes, the attitudes towards robots were more positive in countries with a high proportion of older people.
Overall, though, they found that dislike of robots, at least in Europe, had grown over the past few years – something they concluded should be a warning sign for politicians and business leaders.