Roughness has been scientifically proved to be annoying.{17} Car manufacturers, for instance, have done many studies on how to minimize annoying sounds generated by cars. “One of the biggest factors determining whether a sound will be annoying or not annoying is how smooth the amplitude envelope is,” McDermott says. The envelope is the shape of the amplitude of a sound over time. A rough envelope doesn’t look much like an envelope at all. It looks more like an accordion. If it has that accordion shape—if the volume goes up and down rapidly—the sound tends to annoy people. This might be a factor in why the fingernails-on-chalkboard sound is so annoying: it’s quite rough.
As for why we don’t like roughness, there’s no clear answer. McDermott says, “It’s a bit harder to say why sound roughness is considered unpleasant—as far as we know, it is not harmful to the ears.” David Huron suggests that we don’t like it because rough sounds interfere with our ability to hear, to pull information out of the environment.
The fingernail mystery remains unsolved—but the leads are helpful. Distracting, rough, ear preservation, adapted aversion: these are some of the theories for what makes certain sounds intrinsically unpleasant—explaining their widespread ability to annoy.
4. Skunked
Smells may be the sneakiest of all annoyances. They’re invisible. They’re silent. You are aware of them only after it’s too late. And they’re powerful. Pleasant smells can transport you instantly to a memory of your grandmother’s kitchen or your favorite swimming hole. Unfortunately, unpleasant ones have the same effect.
When you consider that a ten-pound fur ball can ward off a nine-hundred-pound bear simply by suggesting that a bad smell is coming, you realize how powerful odors can be. Think of that for a moment. A porcupine went to the trouble of evolving a coat of razor-sharp spines, and that’s not as effective as a skunk’s primary weapon. Skunks command the forest through smelliness. The aerosol spray isn’t deadly, it’s annoying. It’s so annoying that it can repel almost everything, including much bigger, stronger, and faster predators. For skunks, being annoying means staying alive.
And skunks are deeply annoying. This is clear if you’ve ever had a dog get sprayed by a skunk. It smells terrible—obviously—and before you can bathe your dog, the scent will seemingly have penetrated every object in your house. Even professional groomers can’t completely eliminate the stink from a dog’s coat. Every time you think the odor is gone, it reappears. For days, when you (not your dog) go out wearing clothes that were never anywhere near the skunk or the dog, people will say, “Do you smell a skunk? I thought I caught just the faintest whiff of a skunk in here.”
Skunk spray looks sort of like pizza grease. It’s oily and an orange-yellow color. Skunks produce the spray in their anal glands and turn it into a weapon by shooting it in the direction of predators. Other carnivores, including ferrets, polecats, minks, and weasels, also have the odiferous oil, “but they don’t have the ability to aim and squirt it as skunks do,” says skunk expert Jerry Dragoo.
Skunks have even evolved special anal nipples for spraying! When a skunk feels threatened, “he’s going to aim those nipples, and it’s going to come out like a squirt gun,” says Dragoo, who has been squirted many times in the course of his career as a mephitologist. The term refers to the study of the family Mephitidae, of which skunks are the only members.
Dragoo says that even skunks appear to dislike the odor of skunk spray. This stink also poses a problem for anyone who thinks of becoming a mephitologist. Dragoo says that he can’t smell skunk spray, which may explain his career choice.
William Wood, one of the few chemists brave enough to study skunk spray, suggests that the annoying odor may be responsible for slow advances in the field of skunk spray research. In an article called “The History of Skunk Defensive Secretion Research,” published in the Chemical Educator, Wood wrote, “Skunks and their defensive secretion have both fascinated and repelled natural product chemists. The chemicals secreted by the members of the mephatinae, a New World subfamily of the weasel family (Mustelidae), are so obnoxious that few chemists have been willing to work with them.”{18}
Even if researchers are willing to put up with the odor, their colleagues and neighbors may not be. German scientist and skunk spray pioneer Dr. O. Löw was on an expedition through Texas in the 1870s. He wrote in a letter, “I had frequent opportunity to collect a sufficient quantity of this secretion to establish its chemical constitution, but all my companions protested against it, declaring the odour which clung to me to be unbearable. On my return to New York City I started a few chemical tests, with the little I had collected, when the whole college rose in revolt, shouting, ‘A skunk, a skunk is here!’ I had to abandon the investigation.”
Even in this golden age of fume hoods, studying skunk spray is difficult to do without annoying your colleagues. Wood, of Humboldt State University, was trying to figure out the chemical constituents of skunk spray. That meant collecting samples. “I found dead skunks on the road, and then I put a needle into the duct that had the chemical and pulled it out with a syringe,” he says dryly. “Once you’ve taken a little bit out, the dead skunk would then smell. I would put it in a plastic bag and throw it out the window and then go outside and get it so I wouldn’t smell up the building.”
The fume hood—which is sort of like an oven fan that sucks air out of an enclosed lab bench—worked great at keeping his room odor-free. The problem is that the contaminated air had to go somewhere. It’s usually evacuated from out of the top of the building. This is how Wood discovered who on campus was downwind from him. “The president called me up and said, ‘Are you working with skunks today?’ So I stopped working on skunks at the university.”
Wood started to study skunks because he was interested in chemical ecology: the study of how chemicals carry messages in nature. He says that the field got off the ground about thirty-five years ago, with the study of pheromones—chemical signals that organisms use for communication. Wood has done field research in Africa on the way ticks and tsetse flies use chemicals to communicate; he’s also studied ants in Costa Rica. When he was a postdoc at Cornell University, however, he became attracted to the stench of skunks. “Skunks have the obvious chemical defense that everybody knows about, so I worked on those,” Wood says.
The spray of the striped skunk (Mephitis mephitis) has about seven volatile odor compounds, Wood found. The exact chemical makeup of skunk spray varies from species to species. In all cases, though, the stink is caused by sulfur-laden molecules called thiols. These chemicals, which used to be called mercaptans because of their reactivity with mercury, share similarities in chemical structure to hydrogen sulfide—a toxic compound responsible for the stench of rotten eggs, salt marshes, and bad breath.
Hydrogen sulfide has one sulfur atom and two hydrogen atoms (H2S). If you remove a hydrogen atom and replace it with a carbon one, then you have a thiol. The length of the carbon chain determines the identity of the thioclass="underline" “If you get a thiol on a carbon chain that’s about eight carbons long, it no longer has any odor. It has to be a very short-chain thiol [to smell],” Wood says. Methanethiol is the simplest thiol, with only one carbon (e.g., CH3SH). “Methanethiol and related compounds are produced by the decay of living material,” says chemist Eric Block, of the State University of New York at Albany and author of Garlic and Other Alliums: The Lore and The Science.{19} “Methanethiol has a horrible, stinky, skunky odor to it.”