Dog Bite | Animal Behavior Expert Witness

Richard H. Polsky, Ph.D. CDBC
Los Angeles, California

“Bringing the science of animal behavior to attorneys”

Animal behavior expert on dog bite attacks

Richard H. Polsky, Ph.D. CDBC
Los Angeles, California

“Bringing the science of animal behavior to attorneys”

Dog bite or scratch? – Expert opinion

Occasionally there may be uncertainty about whether the injury inflicted on a person was caused by a dog bite or scratch.  This issue occasionally arises in dog bite litigation. In states which impose strict liability for dog bites, as in Arizona, Florida, California, and Michigan, the claimant can usually successfully sue an owner for damages caused by a bite from the owner’s dog.  However, if the injury was caused by a scratch and not a bite, then no  liability can be imposed on the owner.

In addition, to the “scratch-not-a-bite” defense, there are other defenses to dog bite statues, such as provocation and assumption of risk, and these issues are discussed in other sections of this website.

Below, I respond to correspondence from owners who sought my opinion as to whether the injury was a result of a dog bite vs scratch.

Dog bite or scratch inflicted by a Golden retriever?

Dog bite or scratch
The photograph indicates that the infant most likely was scratched and not bitten by the Golden retriever.

“We’re just trying to figure out what happened to our daughter so we can show that it didn’t happen while in our care. Frankly, I don’t even know if it’ll help at this point. I would appreciate any insight you could give me.  Superficially I’d like to know if you think it looks like dog nail marks. I understand you can’t say for sure, but I need to know if you think it is consistent with how they would look in that situation. The medical trauma and abuse expert says that if the circumstance could support it, and a golden retriever stepped on her head, it could have caused the fracture, hematoma, red mark on the forehead and red nail marks. I’ve been over every other possibility with the trauma expert that we could think of and nothing else reasonably accounts for all the details. For me, its the only explanation that fits, its one of the first things that we were asked when she was seen in the ER, and they simply look like a perfect fit for a dog’s paw. I feel like its common sense, but there’s just no definitive evidence.”

Reply from Dr. Polsky

I agree with you in the fact that the straight horizontal lines are definitely more consistent with an injury inflicted by the dog’s paws rather than its teeth.   And a golden retriever given its size was certainly capable inflicting injuries consistent with what appears in the photograph,  assuming it was a scratch by the dog’s nails.    Before any conclusive opinions can be drawn as to whether the injury was a result of a dog bite or scratch, it would be helpful to know the context in which the injury was inflicted and information about the temperament of the golden retriever.

 Dog the mixed Daschund scratch this lady?

Dog bite or scratch
The photograph suggests, albeit inconclusively, that the victim probably sustained a dog bite inflicted by the Daschund.

“I live in an apartment complex and was walking the dog when she came around the corner. He barked at her and she jumped at him and then she said he bit her. According to her, it was one bite. He is a 12 lb terrier/wiener dog mix and the lady was in her upper 40s maybe 50s. It wasn’t bleeding at first but she messed with it for a few minutes and it started to.”

Reply  from Dr. Polsky

It is not clear whether the scarring is a result of a scratch or  dog bite, but more likely than not, is more consistent with a dog bite because of the curve to the injury and on each end of the scarring it appears that there are two punctures inflicted by a  dog consistent with the size of your dog.  Look closely you will see a single laceration, albeit faint, which has the physical properties of a bite from a small dog.  And this single laceration has a semicircular wound pattern.  Scratch marks are linear in appearance and not circular, as in the example noted above

Did the Jack Russell Terrier bite this man?

Dog bite or scratch
The totality of the evidence suggests the victim was probably bitten by the Jack Russell.

“My dog is a 30 m.o. male rescue Chihuahua/Jack Russel mix.  I got him when he was about 5 months old.  Eddie now weighs approx. 13 lbs.  He is an energetic guy who loves long walks but also spends most of the day sleeping.  He loves to play with balls and soft toys.  I care for an 8-month-old baby. Eddie is jealous when I hold or sit with the baby. He tolerates him well and will play “kickball and chase” as I hold the baby to help him walk.

I live in a condo complex on the 16th floor, so I have trained Eddie to use a potty mat when necessary, but I usually walk him 3-4 times a day and he does most of his business outside.

About 2 months after I got Eddie I was going to walk him one evening before bedtime.  As we exited the elevator on the ground floor, two Golden Doodles belonging to another owner who had let go of the leashes, rushed to Eddie and surrounded him.  Eddie was bitten on his tummy and the next day he was very sick.  The vet stitched up the one puncture would after exploratory surgery to ensure that the tooth had not damaged any internal organs.

Eddie recovered but for about a year afterward, he cowered and whined whenever he saw a larger dog. This gradually changed as Eddie grew older, and he now tends to bark angrily at larger dogs.  He is very friendly toward almost all smaller dogs and will give a friendly sniff to strange dogs and owners we meet on our walks if they are interested.  He usually ignores other dogs if they ignore him.  Eddie loves nothing more than to be petted whether by a friend or most strangers if they approach him gently.

At some point, Eddie started barking at the owner of the Golden Doodles whether he had the dogs with him or not.  The Condo Association had demanded that he muzzle his dogs, carry them to his car and walk them off the property.

Toward the end of last year when I was on the elevator with the baby in the stroller and lightly holding Eddie’s leash, the elevator doors opened unexpectedly on the floor of the owner of the Golden Doodles.  He was standing outside the door holding one of his dogs and Eddie rushed toward him incredibly fast and jumped up against his legs while barking furiously.  I got a hold of Eddie very quickly, but the damage was done, as you can see on the picture. The owner was wearing shorts.

Now the owner claims that Eddie bit him and demands that Eddie wear right now also a muzzle.  I do not think that Eddie bit him at all.  I hope that you can help me determine from the picture whether anything looks like bite wounds or not.

 Reply from Dr. Polsky

Dog expert opinion relies on various sources of evidence to determine with a reasonable degree of certainty whether the injury was caused by a dog bite versus a scratch.

First, a determination needs to be made with regard to the temperament, propensities and motivation of subject dog to inflict a bite in the circumstances that were present when the incident happened. This evidence is gathered from a number of sources such as the behavioral history of the dog, the dog’s relationship with the victim, owner negligence, previous bites inflicted to people, the size of the dog, and obviously the condition of the dog’s teeth and nails.

Second, the physical characteristics of the injury need to be scrutinized. This evidence is most accurately from photographs of the injury taken shortly after the incident happened. Note, information reported by the victim to medical personnel (e.g. emergency room physicians, nurses) needs to be regarded with caution because medical personnel usually enter into the notes simply they are told.

I speculate that the injury was probably caused by a bite and not a scratch:

  • Your Jack Russell mix had obviously formed a negative relationship with the victim. Hence, the motivation was present in your dog to display defensive aggression coupled with biting;
  • The circumstances were present for your dog to react with the defensive type of aggression – that is, the sudden appearance of the man, which likely frighten your dog, when the elevator door opened;
  • The photograph as shown on the top of this page shows two small curves like lacerations. These physical characteristics are consistent with the size of your dog and with injuries caused by a dog bite;
  • The victim may have sustained scratches but it appears that your dog also bit this person.

Example of both scratch and bite wounds to victim riding a bicycle

Dog bite or scratch
Photograph of victim who was riding a bicycle at the time of the incident. The dog was on a leash and jumped at the victim causing both a bite and scratch wounds.

“I was attacked by a dog while riding my bike about 4-5 miles from where I live in Virginia.

 The dog jumped at me from behind and got me near my right hip/buttocks area.

 The dog was on a leash and with his owner but I failed to get the contact info or vaccine records of the dog.

 I am not sure if the wound I have is a dog bite or dog scratch, and I am worried about getting rabies.” 

Reply from Dr. Polsky

Based on the photograph, it looks like you sustained both a single bite from the dog’s canines as well as the scratch.   There appears to be two puncture wounds, horizontally aligned, and there is bruising around the wounds which is typically found in dog bite injury.  The linear line is clearly a scratch and not a bite.It makes sense that the dog would attempt to bite you because he probably was motivated in a predatory sense at the time of the incident, given that you were riding a bicycle  I speculate that the dog probably jumped to inflict a single the bite and in the process inadvertently the nails of one of his paws scratched you.

On the other hand, consider yourself lucky that your injuries were not as serious as they could have been. Fortunately the dog was on a leash and this prevented the dog chasing you. I have had cases where dogs chasing bicycles or motorcycles have caused the rider to crash and as a result the victim sustained broken arms and legs and in another case the victim was not wearing a helmet and suffered brain damage.Note that some dogs have high prey drives and will chase anything given the opportunity. This presents a serious danger to public safety. Owners have the responsibility of keeping dogs with strong prey drives under control at all times, particularly in circumstances where an owner knows their dog may encounter people riding bicycles or motorcycles. Irresponsible owners who allow their dog to engage in predatory type behavior should be financially liable for the injuries their dog may cause to the victim.  However, often this becomes difficult because of the way the laws are written in states without strict liability for dog bites.

The dog was probably owned and therefore probably rabid-free, therefore it’s unlikely the dog was carrying rabies.  Rabies in owned dogs has been practically eradicated in the USA, but nevertheless widespread in countries like China and India where there are a lot of stray dogs running about loose biting people.  It would be inappropriate for me to advise as to whether you should get a rabies shot, other to say than it is unlikely the dog was carrier of rabies.

Scratch versus bite?  Another example of the victim on a bicycle

” I was riding my bicycle earlier this week on the other side of my town in Texas, when a dog began chasing me and eventually inflicted pain on my right leg just above the ankle. Despite looking forward the whole time and not seeing it occur, I was convinced it was a bite because it felt more aggressive than a scratch.

A good example of a dog scratch and not a dog bite. The wound is linear with no jagged edges.

I am worried about rabies because while this dog was not necessarily rabid, it was not on a leash and did not have a collar. The information I had gathered was that it was born at the house I had suspected it belonged to, but ran off and couldn’t be contained. It does however go to that house at a certain time every morning for food. The homeowner described the dog as very skittish, saying it hides under a boat during the day. I have not been given information on its vaccination status.”


Reply from Dr. Polsky

Just looking at the characteristics of the wound  and even in the absence of consideration of the circumstances in which the incident happened, more likely than not  the injury you sustained was  the result of a scratch rather than a bite. The wound is linear and no jagged edges to the wound, both  typical features in a dog scratch wound vs  wound from a dog bite.

More about dog bites vs. injury caused by dog scratch


   Dr. Richard Polsky, a Los Angeles-based dog bite expert witness, welcomes inquiries from attorneys handling cases in which uncertainty exists about whether the injury was inflicted by a dog bite or scratch.  Read about Dr. Polsky’s expert witness consultation services.

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