The plica semilunaris

At the inner corner of our eyes, closest to the nasal ridge, is that little pink thing, which is probably what most of us call it, called the caruncula. Next to it is the plica semilunairs, and it's what's left of a third eyelid that used to — ready for this? — blink horizontally. It's supposed to have offered protection for our eyes, and some birds, reptiles, and fish have such a thing.

Palmaris longus

We don't have much need these days, at least most of us, to navigate from tree branch to tree branch. Still, about 86 percent of us still have the wrist muscle that used to help us do it. To see if you have it, place the back of you hand on a flat surface and touch your thumb to your pinkie. If you have a muscle that becomes visible in your wrist, that's the palmaris longus. If you don't, consider yourself more evolved (just joking).

Darwin's tubercle

Yes, maybe the shell of you ear does feel like a dried apricot. Maybe not. But there's a ridge in that swirly structure that's a muscle which allowed us, at one point, to move our ears in the direction of interesting sounds. These days, we just turn our heads, but there it is.

Goosebumps

It's not entirely clear what purpose made goosebumps worth retaining evolutionarily, but there are two circumstances in which they appear: fear and cold. For fear, they may have been a way of making body hair stand up so we'd appear larger to predators, much the way a cat's tail puffs up — numerous creatures exaggerate their size when threatened. In the cold, they may have trapped additional heat for warmth.

Tailbone

Way back, we had tails that probably helped us balance upright, and was useful moving through trees. We still have the stump of one when we're embryos, from 4–6 weeks, and then the body mostly dissolves it during Weeks 6–8. What's left is the coccyx.

The palmar grasp reflex

You've probably seen how non-human primate babies grab onto their parents' hands to be carried around. We used to do this, too. So still, if you touch your finger to a baby's palm, or if you touch the sole of their foot, the palmar grasp reflex will cause the hand or foot to try and close around your finger.

Other people's suggestions

Amir's followers dove right in, offering both cool and questionable additions to her list.

Fangs?

Lower mouth plate behind your teeth. Some have protruding bone under the skin which is a throw back to large fangs. Almost like an upsidedown Sabre Tooth.

— neil crud (@neilcrud66) January 16, 2019

Hiccups

Sure: https://t.co/DjMZB1XidG

— Stephen Roughley (@SteBobRoughley) January 16, 2019

Hypnic jerk as you fall asleep

What about when you “jump” just as you’re drifting off to sleep, I heard that was a reflex to prevent falling from heights.

— Bann face (@thebanns) January 16, 2019

This thing, often called the "alpha jerk" as you drop into alpha sleep, is properly called the hypnic jerk,. It may actually be a carryover from our arboreal days. The hypothesis is that you suddenly jerk awake to avoid falling out of your tree.

Nails screeching on a blackboard response?

Everyone hate the sound of fingernails on a blackboard. It's _speculated_ that this is a vestigial wiring in our head, because the sound is similar to the shrill warning call of a chimp. https://t.co/ReyZBy6XNN

— Pet Rock (@eclogiter) January 16, 2019

Ear hair

Ok what is Hair in the ears for? I think cuz as we get older it filters out the BS.

— Sarah21 (@mimix3) January 16, 2019

Nervous laughter

You may be onto something. Tooth-bearing with the jaw clenched is generally recognized as a signal of submission or non-threatening in primates. Involuntary smiling or laughing in tense situations might have signaled that you weren’t a threat.

— Jager Tusk (@JagerTusk) January 15, 2019

Um, yipes.

Sometimes it feels like my big toe should be on the side of my foot, was that ever a thing?

— B033? K@($ (@whimbrel17) January 16, 2019

Twitter should always be so much fun.