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Not 100% certain what you mean by "the first move", physically or emotionally? Finding out if a girl likes you isn't really that hard, just look at how they react to your flirting and your "jokes". There is a bit of truth in every joke, which makes it a common way for people to express things they aren't sure they should express. For example, if you make a joke that subtly says, "Let's run away together" and she jokingly says back, "Let's!" there is a good chance she is interested, as opposed to if she says, "But what about my job?" or just "No!" which would imply she might not be so interested.