The secret to protecting your seaside chips from scavenging seagulls is to stare at them, scientists have said.
The birds are more likely to steal food when they can avoid the gaze of their victims, according to a new study.
Researchers at the University of Exeter put a bag of chips on the ground and timed how long herring gulls took to approach when they were being watched.
They compared this to how long it took for the gulls to strike when the person looked away.
The gulls took 21 seconds longer on average when they were being looked at.
The scientists tried to test 74 gulls, but most would not participate.
Of the 27 that approached the chips, 19 completed both the "looking at" and "looking away" tests.
"Gulls are often seen as aggressive and willing to take food from humans, so it was interesting to find that most wouldn't even come near during our tests," said lead author Madeleine Goumas, from of the Centre for Ecology and Conservation at Exeter's Penryn Campus.
"Of those that did approach, most took longer when they were being watched.
"Some wouldn't even touch the food at all, although others didn't seem to notice that a human was staring at them.
She said the more daring seagulls may have had a good experience of being fed by humans, but the study did not examine the reasons for the different responses.
"It seems that a couple of very bold gulls might ruin the reputation of the rest," she added.
Herring gulls are in decline in the UK, but numbers in urban areas are rising, according to experts.
The University of Exeter researchers said the study, conducted in coastal towns in Cornwall and published in the journal Biology Letters, shows how people might be able to reduce food-snatching by modifying their own behaviour.