A viral video of a playful black labrador retriever at the beach is reminding viewers that dogs can leak fluids that are neither urine nor drool. The dog, who seems to be simply enjoying a casual day of sand, surf, and sun, surprises viewers with an unexpected series of spurts: Every time the pup barks, a little bit of liquid surprise squirts out of his beach bum.

When the 2008 video was recently reposted on Reddit, users were confused, with one user calling the dog the “perfect blend of cute, gross and hilarious.” On Monday, another user asked the question that was on everyone’s mind: “Why does the dog shoot water out of his butt when he barks?”

It’s a good question, and not one that’s easily intuited.

The dog’s squirt is similar to the defensive spray that skunks let out when they sense danger. This liquid comes from its anal glands, located on the lower sides of its anus. While dogs can’t release this fluid on command like skunks can, they do sometimes accidentally express the gland when they are excited or frightened — which seems to be the case for this beach-faring pup. Sometimes, squirting even happens spontaneously, according to experts at Putnam North Animal Hospital.

Whatever the cause for its release, the anal gland fluid released from the dog’s butt most likely smells extremely “fishy.” Veterinarians can tell you it’s an oily liquid substance, containing water and bacteria, but they’re not completely sure what the glands do for dogs and the other animals that have them, like cats and bears.

T. J. Dunn, Jr., DVM, in an article on petMD, explains that scientists have narrowed explanations for its existence down to two theories. The first is that its strong scent may be used to help animals mark their territory or as a pheromone for attracting other individuals. The other is that anal gland fluids help dogs poop, especially when hard stool requires some lubrication to be released. Normally, the anal glands release a little bit of fluid whenever a dog poops.

anal gland expression diagram instructions
Sometimes manual expression of the anal gland is necessary.

Occasionally, the fluid in these glands builds up, and the glands need to be expressed manually. If this doesn’t happen, they may become impacted — sort of like an unpopped pimple — and may lead to an infection, which could even require surgery. Sometimes, when dogs drag their butts along the floor (“scooting”), they are really trying to relieve their abscessed anal glands, which can be painful when impacted.

However, since the anal glands are pretty small and the black lab is squirting a lot of fluid, it’s possible he might be squirting more than his natural poop lubricant. The poor pup might also have “beach diarrhea,” which is caused by drinking too much salt water. According to petMD, when dogs drink too much salt water “the [salt-filled] intestines draws water from the blood into the intestines, causing diarrhea.” If the dehydration gets any worse, dogs can have blood and mucous in their diarrhea and can even have a seizure.

Fortunately, it seems unlikely that this adorable lab is super sick, since he happily runs and plays fetch for most of the video. Regardless, his owners, however, might want to look into his involuntary leaking problem, since it could be a sign of an anal gland issue or diarrhea, both of which are decidedly not cute.

Photos via Dummies.com, Flickr / 50-phi