Whenever you go for a walk in the park, you see dog walkers being dragged in all directions by their charges. Sometimes you come across something huge like a Great Dane leading the charge, but as often as not it is a diminutive terrier barking the orders.
Perhaps you have also seen funny videos of giant, docile mutts running in fear from pernicious pups.
We asked our readers if they thought smaller breeds of dog were more aggressive than their larger cousins.
Priyanka Habib got straight to the point. "The tinier they are, the louder and crazier they are!"
The team found that the smaller males "attacked sooner and with greater intensity" than the larger ones
Alan Clark offered an explanation: "I think a lot of small dogs suffer from small dog syndrome. My teacup Yorkie is terrible for confronting big dogs."
It is easy to imagine why "small dog syndrome" might arise. As Travis Souders put it: "They're not necessarily mean, but they're certainly more commonly defensive. How would you feel if you were so tiny?"
Small dog syndrome has a human counterpart in the "Napoleon complex", when someone of diminutive stature compensates by being domineering towards others.
This may make intuitive sense, but research suggests this phenomenon is anecdotal at best.
David Sandberg of The University of Buffalo in New York and Linda Voss of the Peninsula Medical School in Plymouth, UK reviewed the evidence for a Napoleon complex in a study published in 2002. They concluded that "the psychological adaptation of individuals who are shorter than average is largely indistinguishable from others, whether in childhood, adolescence or adulthood."
We see this in nature all the time. Finches and sparrows harassing crows and eagles. Cougars fending off bears. It's not uncommon.
Still, what holds true for humans may not necessarily be the case for animals.
In a study published in 2012, researchers lead by P. Andreas Svensson of Linnaeus University in Sweden tracked the behaviour of fish called desert gobies. Male desert gobies defend nests, so the researchers introduced "intruder" males that the "resident" males had to see off.
The team found that the smaller males "attacked sooner and with greater intensity" than the larger ones.
So if small desert gobies can behave more aggressively than larger ones, could the same be true of dogs?
There is a bit of a leap from a fish to a dog, but as Paul Durnion says: "We see this in nature all the time. Finches and sparrows harassing crows and eagles. Cougars fending off bears. It's not uncommon."
Chunyang Li suggests: "Smaller dogs maybe feel scared about bigger ones, so they always try to protect themselves first of all, showing meaner behaviour."
The problem with small dogs comes from the owners passing on their anxieties to the dogs themselves
In a 2013 paper, Paul McGreevy of the University of Sydney in Australia and his team set out to explore whether dogs' outward characteristics are related to their behaviour.
Dogs were a good species in which to study this, McGreevy wrote, "because skull shapes and body shape are so diverse among breeds". His team tried to find out if dogs that had similar physical traits also behaved similarly.
They found that shorter dogs had higher levels of "owner-directed aggression, begging for food, urine marking and attachment/attention-seeking". In other words, based on this one study smaller dogs really are more aggressive, at least in certain circumstances.
However, the data tells us nothing about why this is.
The researchers concluded that it was "impossible to determine from these data the extent to which the observed relationships are genetically or environmentally determined."
Size might have an influence but it doesn't mean every little dog is vicious
It is certainly possible that smaller dogs have an inbuilt tendency towards aggression, but there are plenty of other potential explanations – most of which have to do with the way humans treat dogs.
"The problem with small dogs comes from the owners passing on their anxieties to the dogs themselves," says Emmet Folens. "They think that as they're small they are prone to be injured by big dogs and generally don't let them socialise as pups."
Alternatively, Hayley Bayles thinks that "owners of small dogs tend to feed their dogs the behaviour by treating them like babies and not actual dogs."
Are they barking up the wrong tree or are they hot on the scent?
McGreevy's study only showed a correlation between size and aggression, not an absolute link, says canine behavioural expert Daniel Mills of Lincoln University in the UK. "Size might have an influence but it doesn't mean every little dog is vicious," he says.
We also do not have good information on which breeds of dog attack the most. "The literature on dog bites suggests you're more likely to report a bite from a German Shepherd than a Jack Russell, because it's a more severe injury," says Mills. "So there's enormous unreliability in [the] available data."
When interacting with little dogs, we may be less aware of early signals of aggression like staring
I wondered if humans might be at fault for, perhaps unwittingly, coercing certain behaviours out of small dogs. Mills says there may be something to that. "People think about these handbag dogs as commodities," he says. "They're as much a status symbol as pit bulls. They're not happy being carried around in handbags and it affects their behavioural development."
In fact there are many ways we can affect canine behaviour. "You often get self-fulfilling prophecies," says Mills. "If a certain behaviour is expected in a dog, it may become tolerated."
We can also be a bit oblivious. "When interacting with little dogs, we may be less aware of early signals of aggression like staring, whereas if a big dog stares and goes still, we think 'I'm not going to approach'," says Mills. "So the first level of what we see in small dogs is something like a snarl, which makes us think they're more aggressive than the bigger dog. [In fact] they're both just saying 'keep away'."
The truth, it seems, is a bit fiddly. There is evidence that smaller dogs tend to be a bit more high-strung than larger dogs, but it may be people that create this difference in behaviour: either by raising small dogs differently, or by misinterpreting their actions.
Maybe keep that in mind the next time you play with a Pomeranian.
Join over five million BBC Earth fans by liking us on Facebook, or follow us on Twitter and Instagram.
If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.