Gravity is related to Fall. Fall is related to Rain. 
Respond is related to Reply. Reply is related to Phrase. Phrase is related to Like. Like is related to String. 
Gravity <--RelatedTo--> Fall <--RelatedTo--> Rain 
Respond <--RelatedTo--> Reply <--RelatedTo--> Phrase <--RelatedTo--> Like <--RelatedTo--> String 