You just know... You know you have natural chemistry with someone when you realize that the days of analyzing every single thing they've said or facial expressions they've made are a thing of the past. When you can be 100% true to yourself, showing you weirdest side without even thinking or a second of second-guessing if it's 'too soon' for that.
When you're both just completely at ease with each other. None of that consciously working towards any couple-goals or milestones. It literally just happens... natural progression.
In my experience, it's really hard to explain. It's just something you feel. It's a spark. I guess some indicators are mutually wanting to spend time together/be with that person all the time, conversations that are full of smiles and laughter, and eye contact. But ultimately it's just something you feel and you just know you have I guess! I know that's pretty ambiguous but I hope it kind of helps!
- you can talk about anything with eachother and conversation still flows - lots of smiling and laughing/joking around - you're comfortable making eye contact with eachother - you just bounce off eachother.. It's hard to describe!