Head is related to Sky. Sky is related to Bird. Bird is related to Airplane. 
Household is related to Fly. Fly is related to Walking. Walking is related to Climb. Climb is related to Dangerous. 
Head <--RelatedTo--> Sky <--RelatedTo--> Bird <--RelatedTo--> Airplane 
Household <--RelatedTo--> Fly <--RelatedTo--> Walking <--RelatedTo--> Climb <--RelatedTo--> Dangerous 