Passion is a synonym of Rage. Rage would make you want to Kill. Brain is a type of Kill. Brain is related to Thought. 
Flat is a synonym of Apartment. you are likely to find Sink in/at/on Apartment. 
Passion <--Synonym--> Rage --CausesDesire--> Kill <--IsA-- Brain <--RelatedTo--> Thought 
Flat <--Synonym--> Apartment <--AtLocation-- Sink 