Two dogs meet, circle, and each sniffs the other’s rear end. To us it is faintly embarrassing. To them it is the informative part of the conversation.
What is being read
The main source is the anal glands — two small sacs either side of the anus that produce a strongly scented secretion. That secretion is chemically individual, and it carries a considerable amount of information:
- Identity. A specific individual, recognisable later
- Sex, and reproductive status — whether a bitch is in season, whether a male is entire
- Approximate age
- Diet, and by extension something about health
- Current emotional state. Stress causes dogs to release more of the secretion, which is why a frightened dog at the vet’s sometimes produces a sudden strong smell
Dogs also read scent from the mouth, ears, genitals and urine. The rear end is simply the richest single source.
The equipment that makes it possible
Dogs have somewhere around 200 to 300 million olfactory receptors, against roughly 5 million in humans. The region of the brain devoted to analysing smell is proportionally about 40 times larger.
They also have a second system we barely use: the vomeronasal organ, or Jacobson’s organ, sitting in the roof of the mouth above the hard palate. It is specialised for detecting pheromones — chemical signals carrying social and reproductive information.
This is what a dog is engaging when they do the odd open-mouthed, slightly grimacing face after sniffing something interesting, sometimes with chattering teeth. The behaviour is called the flehmen response, and horses and cats do a more obvious version of it.
The etiquette of a greeting
There is a proper way for dogs to do this, and it looks nothing like how humans arrange introductions.
Polite:
- Approaching in a curve, not head-on
- Brief sniffing, three or four seconds, then moving on
- Loose bodies, soft eyes, turning the head away at intervals
- Taking turns
- Shaking off afterwards, which releases tension
Rude, in dog terms:
- Walking straight at another dog, face first
- Prolonged direct eye contact
- Standing over the other dog’s shoulders or back
- Stiff, still, tall posture
- Refusing to allow reciprocal sniffing
- Pinning the other dog in place
Most of the trouble at introductions comes from humans arranging exactly the rude version: two dogs on tight leads, head-on, unable to curve away, held in place while the owners chat.
Why lead greetings go wrong
A lead prevents almost everything a dog would do to keep a greeting polite. They cannot curve, they cannot leave, and they cannot control the distance.
Added to that, a tight lead pulls the dog’s front end up and forward into a posture that looks confrontational to the other dog, and the handler’s tension travels straight down it.
Better practice:
- Keep the lead loose
- Approach at an angle, not head-on
- Keep it to three seconds, then cheerfully move on. “Three-second rule” is the standard advice from trainers and it prevents most escalation
- Watch for stiffening, freezing, a high tight tail or a hard stare, and leave before it develops
- Do not force a greeting your dog is avoiding. A dog who turns away has declined
And “he’s friendly” is not a reason to let a dog run up to another dog. Plenty of dogs are not, and the one being approached is the one with no choice.
Sniffing on walks is not time wasted
The other thing dogs read is the ground, and it is the most important part of a walk for them.
Urine marks are an information board: who has been here, when, their sex, their status, their health. A dog reading lamp posts is doing something cognitively substantial.
Research on sniffing has found it lowers heart rate and is associated with more optimistic behaviour in dogs — a twenty-minute sniffing walk tires a dog more than a brisk forty-minute march, and it leaves them calmer rather than more wound up.
So let them sniff. A walk where a dog is marched past everything at heel is exercise for you and frustration for them.
What the nose can do professionally
The same system detects volatile organic compounds at extraordinarily low concentrations, which is why dogs are trained to find explosives, drugs, currency, missing people, truffles, bed bugs and invasive species.
In medical detection, trained dogs have shown the ability to identify samples associated with certain cancers, to alert to imminent hypoglycaemia in diabetic handlers, and in some studies to detect seizures before they occur. The research quality varies, but the underlying capability is not in doubt.
Which is worth remembering when your dog stops to spend a full minute on a patch of grass. They are not being slow. They are reading.
