Yesterday was my birthday. In a misguided attempt to celebrate this auspicious day with me, my first patient of the day took a whopping chomp out of my left hand.

As is my usual style, I made no exclamations or accusations and simply whipped out a muzzle, sparing just enough time to write “Watch!” on the file in bold letters and utter a few words of exculpatory explanations.

Now, this would have been a relatively typical display of appropriate hostility for an animal (in this case, one with painful ears) save for his breed. This was a happy-faced chocolate Lab, not unlike every other Lab I see except in his expert ability to connect teeth to flesh and his uncharacteristic willingness to do so (uncharacteristic for his breed, that is).

Labrador retrievers in our area are almost uniformly even tempered. Sure, some are bouncier than others, but this is the first serious chocolate biter I’ve come across. (24 hours later I’m still nursing a puncture wound at my nail bed and a deep purple bruise in the palm of my hand.)

And yet, there are never any guarantees, as anyone who works with animals knows. Brian Killcommons, a well-known dog trainer and friend of the family once spoke to this point with his sage words: “Dogs are always fine (meaning non-aggressive)…until they’re not.”

Nonetheless, “breedism” is a big deal in vet medicine. Many a mistake has been made in my field by assuming even-temperedness on the basis of breed alone.

Those of you with pit bulls and Rottweilers have doubtless experienced the converse version of this bias, in which muzzles are uniformly applied and heavy-handed holdings are the norm, but few owners of so-called “easy” breeds will relate to this. Their pets are always expected to be saintly examples of their breed.

Luckily, I learned early that this mistake can be costly. The most aggressive pet I’ve yet met was presented to me as an after-hours emergency in my first year out of vet school. But that time there was no mistaking the dog’s intentions:

This Golden retriever wanted me dead. He suffered from “rage,” a descriptive syndrome that seems to have a genetic origin. Though he clearly needed medical attention for a bleeding wound, I was unable to even stand in the same room with him for all his lungings and snarlings.

To make matters worse, the owner was useless. I refused to treat the dog, of course. Living in Philadelphia at the time, I was able to send him to the University of Pennsylvania (with a couple of Acepromazines in his belly) where better resources for handling such examples of his behavioral malady were immediately available (and where I referred him to the behavior service once his laceration was repaired).

Too bad I wasn’t in a similar frame of mind when facing down this chocolate Lab. Memory seems to have a time limit, doesn’t it?

It’s easy for us to flaunt our breed prejudices in veterinary medicine for lack of any political correctness when it comes to preferring one over another. But it’s also stupid to assume anything when it comes to any pet based on his looks alone. Yesterday I received a much-deserved lesson on that fine point. Hopefully this time my memory will serve me a little longer than it did last time.