By Judy Wellsworth

Some foods commonly enjoyed by humans are dangerous to dogs, including chocolate (Theobromine poisoning), onions, grapes and raisins, some types of gum, certain sweeteners and Macadamia nuts. It is currently believed that the only dangerous substance in chocolate is cocoa, meaning that forms of chocolate without this compound, such as white chocolate may become re-evaluated for their safety in future.

The acute danger from grapes and raisins has been uncovered only since about 2000, and made public slowly since then. At present the cause is not known, but one veterinarian believes it may be an acute auto-immune response to plant-borne viruses in the same manner as FIP in cats. Whatever the reason, since only small quantities are necessary to induce acute renal failure, dogs should not be fed grapes or raisins, and sultanas and currants should likely be withheld as well.

Cooked bones should never be given to dogs, as the heat changes the chemical and physical properties so that they cannot be chewed properly, splintering into jagged shards, and resist digestion.

Human medications should not be given to a dog as a substitute for their regular medication as some can be especially toxic, especially paracetamol/acetaminophen (Tylenol). Alcoholic beverages pose much of the same hazards to dogs as they do to humans.

Dogs may also find some poisons attractive, including antifreeze, snail bait, insect bait, and rodent poisons. Antifreeze may be one of the most insidious of poisons to dogs because of its sweet taste and because a dog may walk upon or lie down upon a spill of it or its residue and then lick it off. Dogs must be kept strictly away from antifreeze and not allowed access to any place that has had a spill of it that has not been completely removed.

Plants such as caladium, dieffenbachia and philodendron will cause throat irritations that will burn the throat going down as well as coming up. Hops are particularly dangerous and even small quantities can lead to malignant hyperthermia.

Amaryllis, daffodil, english ivy, iris, and tulip (especially the bulbs) cause gastric irritation and sometimes central nervous system excitement followed by coma, and, in severe cases, even death.

Ingesting foxglove, lily of the valley, larkspur and oleander can be life threatening because the cardiovascular system is affected. Equally life threatening is the yew which affects the nervous system. If any of these plants are ingested, get the dog to a veterinarian immediately.

Many household cleaners such as ammonia, bleach, disinfectants, drain cleaner, soaps, detergents, and other cleaners, mothballs and matches are dangerous to dogs, as are cosmetics such as deodorants, hair coloring, nail polish and remover, home permanent lotion, and suntan lotion.

Zinc toxicity, mostly in the form of the ingestion of US pennies minted after 1982, is commonly fatal in dogs where it causes a severe hemolytic anemia.

Dogs will occasionally eat their own feces or the feces of other species if available, such as that of cats and horses. This is known as coprophagia, and may be indicative of boredom or hunger, although there is no definitive reason known. Owners of both cats and dogs may find that dogs treat the catbox as a snack bar. Such behavior should be discouraged, as it could lead to Toxoplasmosis.

At present, there is some debate as to whether domestic dogs should be classified as omnivores or carnivores, by diet. The classification in the Order Carnivora does not necessarily mean that a dog’s diet must be restricted to meat; unlike an obligate carnivore, such as the cat family with its shorter small intestine, a dog is dependent on neither meat-specific protein nor a very high level of protein in order to fulfill its basic dietary requirements. Dogs are able to healthily digest a variety of foods including vegetables and grains, and in fact can consume a large proportion of these in their diet.

Wild canines not only eat available plants to obtain essential amino acids, but also obtain nutrients from vegetable matter from the stomach and intestinal contents of their herbivorous prey, which they usually consume. Domestic dogs can survive healthily on a reasonable and carefully designed vegetarian diet, particularly if eggs and milk products are included. Some sources suggest that a dog fed on a strict vegetarian diet may develop dilated cardiomyopathy since it lacks L-carnitine, [12] however, maintaining a balanced diet is also a factor since L-carnitine is found naturally in many nuts, seeds, beans, vegetables, fruits and whole grains. In the wild, dogs can survive on a vegetarian diet when animal prey is not available. However it has been noted, both by observation of extremely stressful conditions such as the Iditarod race and by scientific studies of similar conditions, that high-protein (approximately 40%) diets including meat help prevent damage to muscle tissue. (This research is also true for some other mammals.) This level of protein corresponds to the percentage of protein found in the wild dog’s diet when prey is abundant; higher levels of protein seem to confer no added benefit.
Dogs frequently avidly eat grass, which is a harmless activity. Explanations abound, but rationales such as that it neutralizes acid, or that eating grass might make the dog vomit, so dogs eat grass to remove unwanted substances from their stomachs, are at best educated guesses. Dogs do vomit more readily than humans, as part of their typical feeding behavior of gulping down food then regurgitating indigestible bones, fur, etc. This behavior is typical of pack feeding in the wild, where the most important thing is to get as much of the kill as possible before others consume it all. Individual domestic dogs, however, may be very "picky" eaters, in the absence of this evolutionary pressure.

There are several types of working dogs. Including, the detection dog, which is a dog trained to and works at using its senses (almost always the sense of smell) to detect substances such as explosives or illegal drugs.

Hunting dogs that search for game and search dogs that search for missing humans are generally not considered detection dogs. There is some overlap in cases like cadaver dogs that detect human remains. There are other types including the danger dog, war dog and pariah dog.

Dogs have nearly 220 million smell-sensitive cells over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). Some breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren.

What information a dog actually detects when he is scenting is not perfectly understood; although once a matter of debate, it now seems to be well established that dogs can distinguish two different types of scents when trailing, an air scent from some person or thing that has recently passed by, as well as a ground scent that remains detectable for a much longer period. The characteristics and behavior of these two types of scent trail would seem, after some thought, to be quite different, the air scent being intermittent but perhaps less obscured by competing scents, whereas the ground scent would be relatively permanent with respect to careful and repetitive search by the dog, but would seem to be much more contaminated with other scents. In any event, it is established by those who train tracking dogs that it is impossible to teach the dog how to track any better than it does naturally; the object instead is to motivate it properly, and teach it to maintain focus on a single track and ignore any others that might otherwise seem of greater interest to an untrained dog. An intensive search for a scent, for instance searching a ship for contraband, can actually be very fatiguing for a dog, and the dog must be motivated to continue this hard work for a long period of time.

This Collie/Saluki angles her ears to find the source of a sound.
Dogs detect sounds as low as the 16 to 20Hz frequency range (compared to 20 to 70 Hz for humans) and above 45 kHz (compared to 13 to 20 kHz for humans), and in addition have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound. Eighteen or more muscles can tilt, rotate and raise or lower a dog’s ear.

Additionally, a dog can identify a sound’s location much faster than a human can, as well as hear sounds up to four times the distance that humans are able to. Those with more natural ear shapes, like those of wild canids like the fox, generally hear better than those with the floppier ears of many domesticated species.

Amazonian dogs, such as this one from Alto Amazonas, Peru are critical for indigenous peoples’ hunting strategies, particularly in the rain forest.
Dogs were thought to be dichromats and thus, by human standards, color blind. It is now known that dogs can’t see the colour red very well.

Different breeds of dogs have different eye shapes and dimensions, and they also have different retina configurations. Dogs with long noses have a "visual streak" which runs across the width of the retina and gives them a very wide field of excellent vision, while those with short noses have an "area centralis" — a central patch with up to three times the density of nerve endings as the visual streak — giving them detailed sight much more like a human’s.

Some breeds, particularly the best sighthounds, have a field of vision up to 270° (compared to 180° for humans), although broad-headed breeds with short noses have a much narrower field of vision, as low as 180°.

Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws for attacking, holding, and tearing their food.

Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from their distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused wristbones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Compared to the bone structure of the human foot, dogs technically walk on their toes.