When I was about 12 years old, I was standing on my family’s screened porch with our border collie, Nibbles, when a neighbor approached. He smiled, asked if my mother was home, and then pushed open the screen on the door. Nibbles went berserk, barking and snapping and throwing his whole body at the back door.
The neighbor ran down the stairs and left our property. I had never seen Nibbles act so aggressively. Later that summer, the neighbor was arrested and subsequently convicted of 10 counts of child abuse. Nibbles had sensed something sinister about our neighbor and tried to protect his family.
Dogs sometimes don’t like certain people and their owners can’t explain why. But scientists are increasingly learning more about dog behavior and cognition. Since 2005, scientists have studied dogs more intenseand have gained a better understanding of how dogs gather information to determine when someone is growl-worthy.
Sense of smell
When I stood on that screened porch and watched my neighbor approach, I relied mostly on visual cues. Meanwhile, Nibbles was sniffing out the situation.
A dog’s sense of smell is much more sensitive than a human’s. While humans have about five to six million olfactory receptors, dogs do they have 220 million — some breeds have 300 million. Dogs can odor detection that people won’t notice until he concentrates 50 times. In some cases, the scent must be concentrated 100 times before one can detect it.
Studies using nuclear magnetic resonance imaging (MRI) have found that dogs do not have a large frontal lobe like humans. Instead, they have a massive olfactory bulb that takes up 10 percent of their brain.
Because a dog’s sense of smell is 10,000 to sometimes 100,000 times better than ours, dogs can not only smell things that humans can’t register, but they also attach more importance to the smells they smell. While people tend to notice smells that are either good or baddogs collect and store information about all kinds of smells.
In some cases, smells create an association for dogs. in The other end of the strap, applied animal behaviorist describes a dog with whom she worked which welcomed some visitors but bit others. She interviews the client to determine what bite victims have in common. They don’t see any patterns in terms of disliking certain people (ie, fear of tall men), but they can see a similarity in smell among bite victims. They had all eaten pizza before visiting the house, and the dog could still smell it hours later.
As a puppy, a pizza delivery boy kicked the dog, which created a strong association with the smell of pizza and danger. The dog went into defense mode and attacked the human. Knowing the association allowed the behaviorist to retrain the dog to associate the smells of pizza not with kicks but with good things—like trying a few bites.
Sniffing faint odors and forming associations is one way dogs can dislike a person. Research also shows that dogs can smell different human emotions changes in chemosignals, such as adrenaline, sweat and body odor. And when it comes to their people, they can determine whether fear produced sweat.
In a 2018 study Knowledge of animals, researchers collected the sweat of pet parents while watching comedies or horror movies. They randomly assigned the dogs (all Labradors or golden retrievers) to exposure to the scents of fear, happiness, or a control that had no associated chemosignal. They found that dogs exposed to the smell of fear were more focused on their owners and more likely to show a stress response.
Other studies have found that dogs have the ability to sense changes observed in response to fight or flight, including changes in facial expression as well as gestures. Studies have found that service dogs can assisting veterans with post-traumatic stress disorder (PTSD). Dogs can provide a distraction after sensing the slight changes their human exhibits when experiencing intrusive thoughts.
So what got Nibbles going in the summer of 1990? I remember thinking it was odd that the neighbor would come through our back door. It was strange how he came up our stairs and tried to open the screen door. He had never visited us and I did not invite him.
I also distinctly remember the neighbor reaching forward and over his head to push open the door, which may have triggered a fear response in me. Nibbles responded accordingly and the neighbor ran back the way he came.