How do you think a smile can make a difference ?

It matters. It creates a positive vibe around the person smiling and it can be infectious. Kind of infection that is good.

Yupp..it brightens your day

Lately (for the past three months) I’ve been thinking that I was smiling but I made a video of myself and it turns out I haven’t been. When I think I’m smiling the difference to my face is so small it’s indistinguishable from sadness.

Well I think so... I have a crooked smile so people sometimes don't know if I'm making a face or smiling. I try to straighten it when I'm doing a selfie. 😬

Something like 80% of all human communication is non-verbal. - So they say.
And a smile translates into every language.

It spreads good vibes. Of course, it applies when the smile is genuine :)

Smile and find out

I think it buys me a few seconds while I'm reaching for my mace.

Absolutely

Yes

Everyone can smile but not everyone can give genuine smile, that's what matter most

Yes, and yes :)