How can you tell when a girl wants you to grind her?

I cannot tell when someone wants to grind with me or not? Plz help!How can you tell when a girl wants you to grind her?
If she makes a lot of eye contact and is moving her body in a provocative way, then most likely she wants to grind with you. Try to read her body language. If she's moving her hips a lot and smiling, definately go for it. Be careful, though, some girls just want to tease you, and have you watch for a bit.