I believed “bear spray” was a metaphor for a gun. Eg if you were posting online about camping and concerned about the algorithm disliking your use of the word gun, were going into a state park which has guns banned, or didn’t want to mention “gun” for some other reason, then you’d say “bear spray”, since bear spray is such an absurd & silly concept that people will certainly understand what you really mean.

Turns out, bear spray is real. Its pepper spray on steroids, and is actually more effective than a gun, since its easier to aim and is optimized to blind & actually cause pain rather than just damage. [EDIT:] Though see Jimmy's comment below for a counter-point.

I used to think "getting lost in your eyes" was a metaphor, until I made eye contact with particularly beautiful woman in college and found myself losing track of where I was and what I was doing.

these might all be relatively obvious but here are some I've found nice to notice

• brain waves are actual waves of activation that pass through the brain edit: whoops, only partly true. spike trains are only one of the types of neural oscillation referred to by "brain waves"
• our neurons have actual literal weights, having more weight means having more stuff, physically. AI "weights" are named after that edit: this was misremembered, turns out the name origin is probably unrelated - it's only one of quite a number of connection gating mechanisms in the human brain, but dendritic spines do change thickness
• in relativity, spacetime is actually one thing. saying "space and time" is missing the point. though of course until we get a ToE unclear if that model is physically true - but it sure seems like a hint to me
• loud sounds are air smashing your ears [edit: unambiguously well established]
• "I didn't hear that" when people's low level processing fails to parse words someone said despite being perfectly able to receive the audio. not usually playing fool, in my experience [edit: first-hand empirical]

"Seeing the light" to describe having a mystical experience. Seeing bright lights while meditating or praying is an experience that many practitioners have reported, even across religious traditions that didn't have much contact with each other.

One's heart skipping a beat. I thought it was just a poetic way of saying something like "time stood still,"  but no, it turns out it does do that pretty literally.

When I visited Manhattan, I realized that "Wall Street" and "Broadway" are not just overused clichés, but the names of actual streets (you can walk on them!)

On the opposite end, when I was young I learned about the term "Stock market crash", referring to 1929, and I thought literally a car crashed into the physical location where stocks were traded, leading to mass confusion and kickstarting the Great Depression. Though if that actually happened back then, it would have led to a temporary crash in the market.

This feels closely related to Alexithymia or emotion blindness

Extremely common in: people with ADHD / Autism (potentially over half)

Fairly common in: people who have PTSD, people with substance abuse issues (possibly causal, alexithymia -> drugs to feel something), and men (male-normative alexithymia)

People with alexithymia often identify their emotions primarily through physical sensations

For me (a male with autism, ADHD and PTSD) I can tell I'm feeling scared or anxious if my legs get cold (I believe this is a common form)

My example is when people say "I enjoy life" they mean actually enjoying life-as-whole and not like "I'm glad my life is net-positive" or whatever.

If I’ll probably see them again, I don’t miss people. I thought people saying they miss you were just being overly polite.

Feeling pain after hearing a bad joke. "That's literally painful to hear" is self-reportedly (I say in the same way I, without a mind's eye, would say about mind's-eye-people) actually literal for some people.

For most forms of exercise (cardio, weightlifting, HIIT etc.) there's a a spectrum of default experiences people can have from feeling a drug-like high to grindingly unpleasant. "Runner's high" is not a metaphor, and muscle pump while weightlifting can feel similarly good. I recommend experimenting to find what's pleasant for you, though I'd guess valence of exercise is, unfortunately, quite correlated across forms.

Another axis of variation is the felt experience of music. "Music is emotional" is something almost everyone can agree to, but, for some, emotional songs can be frequently tear-jerking and for others that never happens.

I also was kind of surprised when it turned out 'gut feeling' actually meant a feeling in your belly-area.

Added: I wonder if the notion of 'having a hunch' comes from something that causes you to hunch over?

When I first had depression, I remember thinking everything felt dull, like all the color was sucked out of the world, but I thought this was a metaphor even in my own mind.  But then I learned from this post that probably my color perception actually was messed up by depression https://slatestarcodex.com/2017/09/12/toward-a-predictive-theory-of-depression/ 

At a party several years ago an attractive intoxicated person made a pass at me unexpectedly. As a long time married, this isn’t something that happens. At that moment it literally felt like my knees fell out from under me. It was so unlike any other sensation! Im convinced it must have been “weak in the knees”.

I wrote about my own experience discovering “feelings in the body” here

"Home is where the heart is."

I thought this meant something like home is where longing is (your metaphorical heart), the place that you yearn for the most. Now I think it may simply mean that home is wherever your physical beating heart is. The message behind it being that you can adapt to feel at home most anywhere.

"Breathtaking."

I thought this was just an expression to explain natural beauty but I actually felt the breath leave me when I was young from suddenly seeing a sweeping vista of mountains and forest while riding on a bus when I was a teen.

A few people referred to anaxithemia or overcoming it, I think most people don't realize how precise most expressions around feelings are.

"My arms are falling" is an expression in french to explain that you're shocked. I experienced myself my arms becoming impossible to move, as if filled with concrete, after going through some relational shocks (the same is true of "being blinded by X", some extremely intense emotions have literally made me blind for a few secs)

While I'm at it, some mental shocks literally feel like a physical shock! One of those felt for me like an egg being broken against my skull.

"Making nodes in one's head" means overthinking something. "Untying things" means getting helpful insights. However, it's literally what I went through during therapy. There is a literal feeling of untying an invisible "force field", and those nodes are almost always correlated with mental schemes that are uselessly complex. Some people are genuinely worried that you could actively harm your own mental health through overthinking, they're not just finding an excuse for switching topics!

"Vibes" and "vibe" are extremely concrete things for people who got into very special states of consciousness. The french equivalent for that, "ondes", felt so radio-communication related I thought it had to be some telepathy pseudoscience BS. Actually, people are talking about components of subjective perceptions, and some of those (e.g. color, or mood) literally feel/behave like waves when under altered consciousness, and engage in resonance effects as well. To the detriment of the image, however, there seems to be a real contingent that extends this observation to "and we can use them to do telepathy or influence fate".

Sorry, I'm being very pedantic, but how are "picturing" and "mind's eye" not metaphorical? It's not like there's an actual picture or an actual eye anywhere, in fact that's the whole point

I previously thought "Atomic Weapons Establishment" was like "Medical Establishment". But no, the "Atomic Weapons Establishment" is a real organization with buildings that bear that name and employees and a logo and everything somewhere in London.

I was so surprised to hear that that I immediately googled to see if there was a building in Washington DC somewhere that was literally called "The Military Industrial Complex" (there is not).

I am still amazed when I see that uncertainty can be measured.