LET INGA TELL YOU:
I’ve written recently at how dismaying it is to see so many dogs and cats loose in my neighborhood without collars and tags — and as it turns out, without chips either.
A few weeks ago, I kept hearing a cat meowing piteously at my neighbor’s house and queried if their house cat had gotten out by mistake. They texted back that an un-collared cat had shown up and parked itself on their patio furniture clearly wanting food and attention.
The next day, when the cat was still there and still meowing, they concluded it was lost or abandoned, and not wanting to leave it outside for a second night due to a frightening number of coyote sightings and cat deaths in our neighborhood, decided to take it down to the Humane Society. But, as soon as they approached it with the cat carrier, it disappeared through the fence into my yard. We tried to find it to no avail.
A few hours later, I noticed the kitty on my patio. It came right over, allowing me to pick it up. Clearly someone’s pet and not a feral cat. I knew our dog was zonked out in the living room, so I decided to tiptoe in the house with the cat and put it in my office and then text my neighbors to come over with the cat carrier.
Great plan. Utterly failed execution.
I had barely closed the back door behind me when our 19-pound bichon-poodle mix, Lily, woke out of the Sleep of the Canine Dead sensing an intruder in her midst and came charging into the room. I didn’t want to drop the cat right in front of Lily who, despite only having three remaining teeth, seemed determined to use them for harm.
The cat, terrified, alerted me to her wish to be released by sinking her razor-sharp incisors into my hand, then repeating this six more times until I finally got the message.
Lily and the kitty chased each other around the house until I was finally able to corral Lily in a bedroom. My wonderful neighbors came with the cat carrier and lots of Neosporin and took the cat down to the Humane Society.
The Humane Society said it would put the cat in quarantine for 10 days, for both my and their other cats’ protection. I, or my estate, was to call them if I succumbed from feline-related afflictions before then. (OK, that wasn’t exactly the way they put it.)
Searching the Internet, I learned that cat bites have a 40 percent chance of infection and tend to be far more serious than dog bites. I decided that at the slightest sign of infection I would head to urgent care but would keep my multitude of wounds well cleaned, slathered with Neosporin, and wrapped in the meantime.
My husband, Olof, was out of town at the time at the air show in Oshkosh. That night, I e-mailed him: “If a cat bite has a 40 percent chance of infection, do seven cat bites have a 280 percent chance?”
Shortly thereafter, an reply arrived back entitled in pure Olof engineer-ese: “Cat Bite Calculation.” (Note: the La Jolla Light can’t print superscripts, so I’ve written these out as “squared” “cubed” etc.)
You reported earlier that the probability of a cat bite becoming infected was 40 percent (i.e. 40/100 or 2/5). Therefore, the probability that the bite will NOT become infected is 1 – 2/5, or 3/5.
But you didn’t have one bite. You reported seven.
The probability that two bites won’t become infected is the probability that the second won’t, times the probability that the first won’t, or 3/5 x 3/5 = (3/5) squared.
The probability that three bites won’t become infected is the probability that the first two didn’t, times the probability that the third didn’t — i.e. (3/5) squared x 3/5 = (3/5) cubed.
I’m hoping that by now you’re seeing a pattern. The probability that n bites won’t become infected is (3/5) to the nth power; and when n = 7, the reported number of bites you have, the probability is (3/5) to the seventh.
(3/5) to the seventh is approximately 2.8 percent, which is the probability of no infection if the probability of infection of each bite is independent and equal to 40 percent. Alas, this means that the probability of getting an infection is 1 — .028, or about 97 percent.
Fortunately for you, this logic applies only if the chance that one bite will become infected is independent of the chance that any of the others will become infected, which is certainly not the case. If the cat’s mouth is pure, the chance that any will be infected is much much less than 40 percent, and the chance that none will be much higher than 3 percent. Conversely, if the cat has a potty mouth, no math in the world will save you. You’re doomed.
To be continued next week ...
— Inga’s lighthearted looks at life appear regularly in La Jolla Light. Reach her at firstname.lastname@example.org