sentences: if two objects are rubbing each other, then they are moving against each other
docs: rubbing is friction. humans_touching_each_other is situation_involving_physical_contact. deliberately_touching is touching. butting_against is touching. abrading_event is rubbing. touching is touching. touching is event_involving_physical_contact. hugging is humans_touching_each_other. if rub occurs then touch occurs. massage is rubbing.