Appropriate is related to Proper. Proper is the opposite of Wrong. Killing can be Wrong. Killing requires Rage. 
Vocal is related to Mouth. Trap is a type of Mouth. Trap is a type of Capture. Capture is a synonym of Appropriate. 
Appropriate <--RelatedTo--> Proper <--Antonym--> Wrong <--HasProperty-- Killing --HasPrerequisite--> Rage 
Vocal <--RelatedTo--> Mouth <--IsA-- Trap --IsA--> Capture <--Synonym--> Appropriate 