According to a recent (and extremely compelling) case study performed by a team of dentists in Mexico, a 47-year-old man developed a circular wound on the roof of his mouth after sucking too much dick—proving that you can have (or, y’know, give) too much of a good thing.

“The contact of the palate with the penile glands [glans?] may cause a hematoma due to blunt trauma and dilatation of the blood vessels because of the negative pressure created while sucking,” Luis Alberto Mendez, who treated the patient, writes in the study. “With this information, we concluded that the erythema on the soft palate was associated with the practice of oral sex.”

The man reportedly performed oral sex only three days before his appointment, which reminded me of an old schoolyard rumor that dentists can tell when you’ve given a beej within close proximity to your visit. Upon further investigation, that rumor may actually hold true in some instances.

While the wound reported in this case study is relatively rare, the authors note that a previous report of 132 sex workers in Peru found that 17 suffered from similar lesions in the mouth caused by oral sex, suggesting that this specific type of wound might indicate to your dentist that you recently engaged in an epic blowjob session. Another 2013 report found lesions on the palate of a young woman that were similarly thought to be associated with fellatio.

A blog post by cosmetic and family dentist Soft Dental identifies a common type of wound associated with oral sex as “purpuric macule,” which they say “is produced by a blunt traumatic insult to the skin or mucosa of sufficient force to cause the discharge of blood on the surface.” The post goes on to explain how sucking dick may result in such a purpuric macule: “This condition may be the result from oral sexual practices, when the repeated bumping of the male organ traumatizes on the soft tissue this region. In such a case the lesion disappears within 2 or 3 days, only to return again when the act is recur [sic].”

In other words, if you deepthroated some big dick within approximately three days of your appointment, your dentist might be able to guess what went down when you show up with a purpuric macule.

It’s worth noting, however, that identifying whether or not patients engage in oral sex is neither the purpose of your dental examination, nor a standard part of the process, so it’s not like a dentist is looking for this kind of evidence right off the bat. And even if such a wound were found, dentists would first have to examine your lifestyle before coming to the conclusion that your problems were 100 percent caused by fellatio. As the American Dental Association explained to me by email: “During a standard dental exam, a dentist cannot determine if a patient regularly engages in oral sex. However, a dentist is trained to notice abnormalities in the mouth and can discuss with a patient what may be causing them.” So that’s reassuring.

Still, while we’re speculating, let’s remember that we also recently wrote about how sperm could theoretically survive in your mouth for several days. So theoretically, your dentist might know you’ve been gobbling choad if they were to swab the inside of your mouth for a closer look under a microscope:

“‘If you’re talking about the science behind it, the temperature of the mouth is warmer than outside the body, and it’s a mucosal substance with gums, nooks and crannies,’ Brian Steixner, a urologist and director of the Institute of Men’s Health at Jersey Urology Group, told Men’s Health. ‘In theory, it’s 100 percent reasonable that a sperm from oral sex in someone’s mouth could be alive the day after, assuming it’s Monday, or two days later.’ Board-certified urologist Jamin Brahmbhatt agrees, adding that what we know about vaginal tissue can be generalized to include oral tissue.”

All of which goes a long way toward explaining why dentists always tell you to spit.