What causes playful teasing/flirting between a guy and girl?

I’ve met a guy and we get on really well, we have been talking every day and we have lots of cheeky banter and teasing.
When we met in person it was the same and it didn’t take long for us to playfully tease and joke with each other.
Things are so easy and natural with us and we both seem to be on the same wavelength.
I’m sure it is but Id just like opinions if playful teasing is a sign of sexual tension/attraction?
What causes playful teasing/flirting between a guy and girl?
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