Why Popcorn Smells Like A Bearcat's Butt - National Geographic

Story’s paper was an effort to set naturalists straight on binturong anal glands. Three decades earlier, British zoologist Reginald Innes Pocock described and illustrated the genitals and scent glands of the bearcat, but, when Story looked at several dead animals donated to the Chicago Natural History Museum by the Chicago Zoological Society, she found that “[Pocok’s] drawings, admittedly somewhat diagrammatic, prove to be extremely misleading.” Likewise, other previous studies had suggested that the position of the anal glands shifted as the animals grew up. Story did not find evidence of any change in placement among the specimens in her collection, and she lamented “The problems arising from the confused state of the literature on the civets.” Was there no respect for the anatomy of viverrid rumps?

In both male and female binturongs, Story found, the “perfume gland” was only visible as a swelling in the vicinity of the genitals. In males, the gland was a U-shaped pad which sat between the penis and scrotum, and in females the gland was divided into two halves — which looked like a pair of parentheses — underlying either side of the vulva. And, in both sexes, the ducts of these glands led to openings on either side of the anus. That’s where the popcorn scent is coming from.

Devra Kleiman described how binturongs went about applying this scent in a 1974 paper based on observations of a captive animals at the National Zoo. The keepers wanted some baby binturongs, but couldn’t figure out how to get their animals to show anything more than a passing interest in each other. The paper came out of observations of the binturongs after one female had been given pregnant mare’s serum gonadotropin — a substance extracted from the blood of gravid horses used to stimulate the ovaries of other animals — in an effort to pique her interest in her potential mate.

Kleiman pointed out that binturongs left scent behind while climbing and sitting, but the mammals also engaged in deliberate scent-marking behavior. Whether on the ground, upside down, or hanging vertically, the binturongs scuffed their feet on the surface they were about to mark and then dragged their anal gland over the surface. (Kleiman called the inverted behavior “an upside-down perineal drag,” which also sounds like a suitable alternate description for an excruciatingly boring event. “Hey, did you catch the latest Republican debate?” “Ugh, it was such an upside-down perineal drag.”) All of this is advertising. You might leave a business card; a binturong drags their ass over whatever it is they want to carry their message.

Based on Kleiman’s observations, binturongs seemed to take almost any excuse to scent mark. That pole not as stinky as it used to be? Scent mark. Feeding time? Scent mark. An unfamiliar human comes by? Scent mark.  Smell is essential to these animals, and that’s especially true during the mating process.