Pot-dar, it's sort of like gay-dar but not. It accurately describes the phenomena at parties when the weed comes out. No one ever says "Hey we are smoking weed now, come over if you want some", instead somehow people gravitate to the said area and commit the act (one of which I am neither condeming or encouraging). There must be some sort of internal GPS system that goes off sending messages to the brain, "psst, pot other there, go, RUN!". Other theories include Y shaped sticks that point in the direction of the desired object or if you wish it, it will happen. Or there could be a simple explanation. People smell it and then head on over.