How do you know if a girl wants to grind at a club?

What I have been doing previously is just dance with the girls, make some eye contact and then start with salsa dancing and then transition to back grind. This has worked maybe 10% of the time. What are girls thinking? How can I make it more likely that girls will grind with me?

Also please no remarks about being shallow. This is simply nature.
How do you know if a girl wants to grind at a club?
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