Staring at seagulls stops them stealing your chips, according to new research.
The scavenging birds are a nightmare for holidaymakers and tourists flocking to the coast - even snatching ice cream from their hands.
Now scientists reckon they have come up with a simple solution - which is to look them straight in the eyes.
They put a bag of chips on the ground as bait and tested how long it took herring gulls to approach.
With a human watching, this was an average 21 seconds more than when they looked away with most keeping well away.
Lead author Madeleine Goumas, of the Centre for Ecology and Conservation at Exeter University's Penryn Campus in Cornwall, said: "Gulls are often seen as aggressive and willing to take food from humans.
"So it was interesting to find most wouldn't even come near during our tests."
Herring gulls, the most familiar of Britain's seagulls, have a bad reputation for pinching people's grub.
So postgraduate student Miss Goumas and colleagues tempted them in coastal towns with chips to see if staring reduced their attempts to pilfer.
Gulls approached more slowly or not at all when they were being watched. But many approached within seconds when the experimenter looked away.
Miss Goumas said: "By keeping an eye on gulls, people could potentially save their lunch while reducing negative encounters with this rapidly declining species."
Her team attempted to test 74 birds along the Cornish coast but most flew away, with just 27 approaching the food.
The study published in the Royal Society's Biology Letters focused on the 19 that completed both the "looking at" and "looking away" tests.
Miss Goumas said: "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.
"We didn't examine why individual gulls were so different - it might be because of differences in 'personality' and some might have had positive experiences of being fed by humans in the past."
She added: "But it seems that a couple of very bold gulls might ruin the reputation of the rest."
The species is on the UK's Red list of Birds of Conservation Concern. The British population fell by 60 percent between 1969 and 2015 with plastic pollution blamed.
Senior author Dr Neeltje Boogert said: "Gulls learn really quickly, so if they manage to get food from humans once, they might look for more.
"Our study took place in coastal towns in Cornwall, and especially now, during the summer holidays and beach barbecues, we are seeing more gulls looking for an easy meal.
"We therefore advise people to look around themselves and watch out for gulls approaching, as they often appear to take food from behind, catching people by surprise.
"It seems that just watching the gulls will reduce the chance of them snatching your food."
While herring gulls are in decline, the numbers in urban areas are rising. Gulls in these areas are often considered a nuisance because of food-snatching and other anti social behaviour.
Miss Goumas said the study shows any attempt to manage the issue by treating all gulls as being alike could be futile, as most are wary of approaching people.
Instead, people might be able to reduce a problem caused by a few bold individuals by changing their own behaviour, such as being more vigilant.
The natural diet of herring gulls is fish and invertebrates. The researchers now plan to investigate how eating human foods affects the gulls, and their chicks, in the long term.
Miss Goumas said: "Conflict between herring gulls and humans is an ongoing source of debate and control measures.
"Herring gulls in urban environments appear to have generalised their kleptoparasitic activities to target humans, resulting in numerous complaints to local authorities and
increasing human–herring gull conflict."
Lethal control or deterrents, by using birds of prey to kill them, for example, often prove costly and ineffective and ignore specific behaviour, she said.
Added Miss Goumas: "Our results indicate the majority of urban herring gulls are unlikely to approach food when humans are nearby.
"Those gulls that did approach responded to subtle behavioural cues from the experimenter, suggesting increased vigilance by humans may reduce food snatching behaviour.
"Understanding individual variation in behaviour, and responses towards human behavioural cues more generally, may help inform conservation and control strategies for managing conflict between humans and wildlife in a wide range of taxa."