What are the signs that you have chemistry with a guy?

I'm curious cause I've been on a lot of dates before in the past and I know all the questions to ask to get the date going but there's been very few dates where I can't think of anything to say nor the guy. Maybe that's not chemistry? I'm just wondering how you know if you have real good chemistry with a guy.
What are the signs that you have chemistry with a guy?
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