The 'plica fimbriata' fringes on the underside of the tongue

Lift your tongue in a mirror and you might notice some jagged, fleshy fringes running along the bottom. They look like a manufacturing defect or a piece of lace trim that’s starting to unravel.

These are the plica fimbriata. Think of them as a ghost feature from an older version of the human operating system that evolution forgot to patch out.

In our distant primate ancestors, these were part of a rigid sub-tongue used as a built-in comb for grooming fur. We lost the fur, but the body kept the grooming kit, leaving these weird little tassels behind for no reason at all.

Wait, so do some animals still have a fully functional second tongue?

Oh, absolutely. If you look at a lemur, you’re seeing the 'Pro' version of your glitchy hardware. They have a literal second tongue called a sublingua—a stiff, jagged plate that sits right under the soft, muscular main tongue like a specialized attachment on a multi-tool.

It functions as a high-pressure cleaning kit. Lemurs have front teeth shaped like a literal hair comb. After a heavy grooming session, those teeth get clogged with fur and debris. The sublingua slides in to scrape the gunk out so the animal doesn't end up with a mouth full of felt.

In humans, the 'sublingua.exe' file was mostly deleted during an update. We’re left with the plica fimbriata—the digital artifacts of a grooming tool we no longer have the fur to use. It’s like keeping a legacy printer driver on a laptop that doesn't even have a USB port.

Hold on, how do those comb-teeth even fit inside a mouth?

It’s a clever hardware mod. In lemurs, the lower front teeth don’t grow straight up like ours; they tilt forward horizontally, forming a flat, serrated shelf that sits flush with the bottom of the mouth.

Imagine your bottom teeth re-aligning into a row of fine-toothed needles. It’s perfect for raking through matted fur to pick out parasites, but it’s a terrible design for biting into anything solid.

Humans eventually "uninstalled" this grooming kit because we developed hands. Once you have nimble fingers, you don't need to turn your face into a specialized garden rake to stay clean.

But if their front teeth are combs, how do they manage to eat?

It’s like trying to eat a steak with a fine-toothed lice comb. You simply don't. Those front teeth are so specialized for grooming that they’re practically useless for a standard 'bite' into a piece of fruit.

To compensate for this hardware limitation, lemurs have to use their premolars—the teeth further back—as their primary cutters. They basically shove food into the side of their mouths like a person trying to eat while wearing a very expensive, very fragile set of vampire fangs.

It’s a classic evolutionary compromise: they traded the ability to nip and bite with their front teeth for the convenience of never needing a trip to the primate barber.

Does this side-eating thing mean they can only eat soft mushy stuff?

You’d think they’d be stuck on a smoothie diet, but evolution found a workaround. Since they can’t 'snip' fruit with their front teeth, they use their premolars like heavy-duty bolt cutters.

They jam food into the corner of their mouth and let the back teeth do the shearing. It’s not elegant—it looks like eating a burrito sideways—but it works.

They even eat tough bark this way. They just bypass the 'front-end' processing entirely. It’s a clunky UI, but the backend hardware is surprisingly powerful.